This module implements a variety of type constructors, i.e., templates that allow construction of new, useful general-purpose types.
| Category | Functions |
|---|---|
| Tuple | isTuple Tuple tuple reverse |
| Flags | BitFlags isBitFlagEnum Flag No Yes |
| Memory allocation | RefCounted refCounted RefCountedAutoInitialize scoped Unique |
| Code generation | AutoImplement BlackHole generateAssertTrap generateEmptyFunction WhiteHole |
| Nullable | Nullable nullable NullableRef nullableRef |
| Proxies | Proxy rebindable Rebindable ReplaceType unwrap wrap |
| Types | alignForSize Ternary Typedef TypedefType UnqualRef |
// value tuples
alias Coord = Tuple!(int, "x", int, "y", int, "z");
Coord c;
c[1] = 1; // access by index
c.z = 1; // access by given name
writeln(c); // Coord(0, 1, 1)
// names can be omitted
alias DicEntry = Tuple!(string, string);
// tuples can also be constructed on instantiation
writeln(tuple(2, 3, 4)[1]); // 3
// construction on instantiation works with names too
writeln(tuple!("x", "y", "z")(2, 3, 4).y); // 3
// Rebindable references to const and immutable objects
{
class Widget { void foo() const @safe {} }
const w1 = new Widget, w2 = new Widget;
w1.foo();
// w1 = w2 would not work; can't rebind const object
auto r = Rebindable!(const Widget)(w1);
// invoke method as if r were a Widget object
r.foo();
// rebind r to refer to another object
r = w2;
}
Encapsulates unique ownership of a resource.
When a Unique!T goes out of scope it will call destroy on the resource T that it manages, unless it is transferred. One important consequence of destroy is that it will call the destructor of the resource T. GC-managed references are not guaranteed to be valid during a destructor call, but other members of T, such as file handles or pointers to malloc memory, will still be valid during the destructor call. This allows the resource T to deallocate or clean up any non-GC resources.
If it is desirable to persist a Unique!T outside of its original scope, then it can be transferred. The transfer can be explicit, by calling release, or implicit, when returning Unique from a function. The resource T can be a polymorphic class object or instance of an interface, in which case Unique behaves polymorphically too.
If T is a value type, then Unique!T will be implemented as a reference to a T.
static struct S
{
int i;
this(int i){this.i = i;}
}
Unique!S produce()
{
// Construct a unique instance of S on the heap
Unique!S ut = new S(5);
// Implicit transfer of ownership
return ut;
}
// Borrow a unique resource by ref
void increment(ref Unique!S ur)
{
ur.i++;
}
void consume(Unique!S u2)
{
writeln(u2.i); // 6
// Resource automatically deleted here
}
Unique!S u1;
assert(u1.isEmpty);
u1 = produce();
increment(u1);
writeln(u1.i); // 6
//consume(u1); // Error: u1 is not copyable
// Transfer ownership of the resource
consume(u1.release);
assert(u1.isEmpty);
Represents a reference to T. Resolves to T* if T is a value type.
Allows safe construction of Unique. It creates the resource and guarantees unique ownership of it (unless T publishes aliases of this).
A args
| Arguments to pass to T's constructor. static class C {}
auto u = Unique!(C).create();
|
Constructor that takes an rvalue. It will ensure uniqueness, as long as the rvalue isn't just a view on an lvalue (e.g., a cast). Typical usage:
Unique!Foo f = new Foo;
Constructor that takes an lvalue. It nulls its source. The nulling will ensure uniqueness as long as there are no previous aliases to the source.
Constructor that takes a Unique of a type that is convertible to our type.
Typically used to transfer a Unique rvalue of derived type to a Unique of base type.
class C : Object {}
Unique!C uc = new C;
Unique!Object uo = uc.release;
Transfer ownership from a Unique of a type that is convertible to our type.
Returns whether the resource exists.
Transfer ownership to a Unique rvalue. Nullifies the current contents. Same as calling std.algorithm.move on it.
Tuple of values, for example Tuple!(int, string) is a record that stores an int and a string. Tuple can be used to bundle values together, notably when returning multiple values from a function. If obj is a Tuple, the individual members are accessible with the syntax obj[0] for the first field, obj[1] for the second, and so on.
The choice of zero-based indexing instead of one-base indexing was motivated by the ability to use value tuples with various compile-time loop constructs (e.g. std.meta.AliasSeq iteration), all of which use zero-based indexing.
tuple. | Specs | A list of types (and optionally, member names) that the Tuple contains. |
Tuple!(int, int) point; // assign coordinates point[0] = 5; point[1] = 6; // read coordinates auto x = point[0]; auto y = point[1];
Tuple members can be named. It is legal to mix named and unnamed members. The method above is still applicable to all fields. alias Entry = Tuple!(int, "index", string, "value"); Entry e; e.index = 4; e.value = "Hello"; writeln(e[1]); // "Hello" writeln(e[0]); // 4
Tuple with named fields is a distinct type from a Tuple with unnamed fields, i.e. each naming imparts a separate type for the Tuple. Two Tuples differing in naming only are still distinct, even though they might have the same structure. Tuple!(int, "x", int, "y") point1; Tuple!(int, int) point2; assert(!is(typeof(point1) == typeof(point2)));
The types of the Tuple's components.
alias Fields = Tuple!(int, "id", string, float); static assert(is(Fields.Types == AliasSeq!(int, string, float)));
The names of the Tuple's components. Unnamed fields have empty names.
alias Fields = Tuple!(int, "id", string, float);
static assert(Fields.fieldNames == AliasSeq!("id", "", ""));
Use t.expand for a Tuple t to expand it into its components. The result of expand acts as if the Tuple's components were listed as a list of values. (Ordinarily, a Tuple acts as a single value.)
auto t1 = tuple(1, " hello ", 2.3);
writeln(t1.toString()); // `Tuple!(int, string, double)(1, " hello ", 2.3)`
void takeSeveralTypes(int n, string s, bool b)
{
assert(n == 4 && s == "test" && b == false);
}
auto t2 = tuple(4, "test", false);
//t.expand acting as a list of values
takeSeveralTypes(t2.expand);
Constructor taking one value for each field.
Types values
| A list of values that are either the same types as those given by the Types field of this Tuple, or can implicitly convert to those types. They must be in the same order as they appear in Types. |
alias ISD = Tuple!(int, string, double); auto tup = ISD(1, "test", 3.2); writeln(tup.toString()); // `Tuple!(int, string, double)(1, "test", 3.2)`
Constructor taking a compatible array.
U[n] values
| A compatible static array to build the Tuple from. Array slices are not supported. |
int[2] ints; Tuple!(int, int) t = ints;
Constructor taking a compatible Tuple. Two Tuples are compatible iff they are both of the same length, and, for each type T on the left-hand side, the corresponding type U on the right-hand side can implicitly convert to T.
U another
| A compatible Tuple to build from. Its type must be compatible with the target Tuple's type. |
alias IntVec = Tuple!(int, int, int); alias DubVec = Tuple!(double, double, double); IntVec iv = tuple(1, 1, 1); //Ok, int can implicitly convert to double DubVec dv = iv; //Error: double cannot implicitly convert to int //IntVec iv2 = dv;
Comparison for equality. Two Tuples are considered equal iff they fulfill the following criteria:
Tuple is the same length.T on the left-hand side and each type U on the right-hand side, values of type T can be compared with values of type U.v1 on the left-hand side and each value v2 on the right-hand side, the expression v1 == v2 is true.R rhs
| The Tuple to compare against. It must meeting the criteria for comparison between Tuples. |
true if both Tuples are equal, otherwise false.Tuple!(int, string) t1 = tuple(1, "test"); Tuple!(double, string) t2 = tuple(1.0, "test"); //Ok, int can be compared with double and //both have a value of 1 writeln(t1); // t2
Comparison for ordering.
R rhs
| The Tuple to compare against. It must meet the criteria for comparison between Tuples. |
v1 on the right-hand side and v2 on the left-hand side: v1 < v2 is true.v1 > v2 is true.v1 == v2 is true.v1 for which v1 > v2 is true determines the result. This could lead to unexpected behaviour. auto tup1 = tuple(1, 1, 1); auto tup2 = tuple(1, 100, 100); assert(tup1 < tup2); //Only the first result matters for comparison tup1[0] = 2; assert(tup1 > tup2);
Assignment from another Tuple.
R rhs
| The source Tuple to assign from. Each element of the source Tuple must be implicitly assignable to each respective element of the target Tuple. |
Renames the elements of a Tuple.
rename uses the passed names and returns a new Tuple using these names, with the content unchanged. If fewer names are passed than there are members of the Tuple then those trailing members are unchanged. An empty string will remove the name for that member. It is an compile-time error to pass more names than there are members of the Tuple.
auto t0 = tuple(4, "hello");
auto t0Named = t0.rename!("val", "tag");
writeln(t0Named.val); // 4
writeln(t0Named.tag); // "hello"
Tuple!(float, "dat", size_t[2], "pos") t1;
t1.pos = [2, 1];
auto t1Named = t1.rename!"height";
t1Named.height = 3.4f;
writeln(t1Named.height); // 3.4f
writeln(t1Named.pos); // [2, 1]
t1Named.rename!"altitude".altitude = 5;
writeln(t1Named.height); // 5
Tuple!(int, "a", int, int, "c") t2;
t2 = tuple(3,4,5);
auto t2Named = t2.rename!("", "b");
// "a" no longer has a name
static assert(!hasMember!(typeof(t2Named), "a"));
writeln(t2Named[0]); // 3
writeln(t2Named.b); // 4
writeln(t2Named.c); // 5
// not allowed to specify more names than the tuple has members
static assert(!__traits(compiles, t2.rename!("a","b","c","d")));
// use it in a range pipeline
import std.range : iota, zip;
import std.algorithm.iteration : map, sum;
auto res = zip(iota(1, 4), iota(10, 13))
.map!(t => t.rename!("a", "b"))
.map!(t => t.a * t.b)
.sum;
writeln(res); // 68
Overload of rename that takes an associative array translate as a template parameter, where the keys are either the names or indices of the members to be changed and the new names are the corresponding values. Every key in translate must be the name of a member of the tuple. The same rules for empty strings apply as for the variadic template overload of rename.
//replacing names by their current name Tuple!(float, "dat", size_t[2], "pos") t1; t1.pos = [2, 1]; auto t1Named = t1.rename!(["dat": "height"]); t1Named.height = 3.4; writeln(t1Named.pos); // [2, 1] t1Named.rename!(["height": "altitude"]).altitude = 5; writeln(t1Named.height); // 5 Tuple!(int, "a", int, "b") t2; t2 = tuple(3, 4); auto t2Named = t2.rename!(["a": "b", "b": "c"]); writeln(t2Named.b); // 3 writeln(t2Named.c); // 4
//replace names by their position Tuple!(float, "dat", size_t[2], "pos") t1; t1.pos = [2, 1]; auto t1Named = t1.rename!([0: "height"]); t1Named.height = 3.4; writeln(t1Named.pos); // [2, 1] t1Named.rename!([0: "altitude"]).altitude = 5; writeln(t1Named.height); // 5 Tuple!(int, "a", int, "b", int, "c") t2; t2 = tuple(3, 4, 5); auto t2Named = t2.rename!([0: "c", 2: "a"]); writeln(t2Named.a); // 5 writeln(t2Named.b); // 4 writeln(t2Named.c); // 3
Takes a slice by-reference of this Tuple.
| from | A size_t designating the starting position of the slice. |
| to | A size_t designating the ending position (exclusive) of the slice. |
Tuple that is a slice from [from, to) of the original. It has the same types and values as the range [from, to) in the original.Tuple!(int, string, float, double) a; a[1] = "abc"; a[2] = 4.5; auto s = a.slice!(1, 3); static assert(is(typeof(s) == Tuple!(string, float))); assert(s[0] == "abc" && s[1] == 4.5); // Phobos issue #15645 Tuple!(int, short, bool, double) b; static assert(!__traits(compiles, b.slice!(2, 4)));
Creates a hash of this Tuple.
size_t representing the hash of this Tuple.Converts to string.
Tuple.Formats Tuple with either %s, %(inner%) or %(inner%|sep%).
| Format | Description |
|---|---|
|
Format like |
|
The format |
|
The format |
Tuple!(int, double)[3] tupList = [ tuple(1, 1.0), tuple(2, 4.0), tuple(3, 9.0) ];
// Default format
assert(format("%s", tuple("a", 1)) == `Tuple!(string, int)("a", 1)`);
// One Format for each individual component
assert(format("%(%#x v %.4f w %#x%)", tuple(1, 1.0, 10)) == `0x1 v 1.0000 w 0xa`);
assert(format( "%#x v %.4f w %#x" , tuple(1, 1.0, 10).expand) == `0x1 v 1.0000 w 0xa`);
// One Format for all components
assert(format("%(>%s<%| & %)", tuple("abc", 1, 2.3, [4, 5])) == `>abc< & >1< & >2.3< & >[4, 5]<`);
// Array of Tuples
assert(format("%(%(f(%d) = %.1f%); %)", tupList) == `f(1) = 1.0; f(2) = 4.0; f(3) = 9.0`);
// Error: %( %) missing.
assertThrown!FormatException(
format("%d, %f", tuple(1, 2.0)) == `1, 2.0`
);
// Error: %( %| %) missing.
assertThrown!FormatException(
format("%d", tuple(1, 2)) == `1, 2`
);
// Error: %d inadequate for double.
assertThrown!FormatException(
format("%(%d%|, %)", tuple(1, 2.0)) == `1, 2.0`
);
Creates a copy of a Tuple with its fields in reverse order.
T t
| The Tuple to copy. |
Tuple.auto tup = tuple(1, "2");
writeln(tup.reverse); // tuple("2", 1)
Constructs a Tuple object instantiated and initialized according to the given arguments.
| Names | An optional list of strings naming each successive field of the Tuple. Each name matches up with the corresponding field given by Args. A name does not have to be provided for every field, but as the names must proceed in order, it is not possible to skip one field and name the next after it. |
auto value = tuple(5, 6.7, "hello");
writeln(value[0]); // 5
writeln(value[1]); // 6.7
writeln(value[2]); // "hello"
// Field names can be provided.
auto entry = tuple!("index", "value")(4, "Hello");
writeln(entry.index); // 4
writeln(entry.value); // "Hello"
Args args
| Values to initialize the Tuple with. The Tuple's type will be inferred from the types of the values given. |
Tuple with its type inferred from the arguments given.Returns true if and only if T is an instance of std.typecons.Tuple.
| T | The type to check. |
true if T is a Tuple type, false otherwise.static assert(isTuple!(Tuple!())); static assert(isTuple!(Tuple!(int))); static assert(isTuple!(Tuple!(int, real, string))); static assert(isTuple!(Tuple!(int, "x", real, "y"))); static assert(isTuple!(Tuple!(int, Tuple!(real), string)));
Rebindable!(T) is a simple, efficient wrapper that behaves just like an object of type T, except that you can reassign it to refer to another object. For completeness, Rebindable!(T) aliases itself away to T if T is a non-const object type.
You may want to use Rebindable when you want to have mutable storage referring to const objects, for example an array of references that must be sorted in place. Rebindable does not break the soundness of D's type system and does not incur any of the risks usually associated with cast.
| T | An object, interface, array slice type, or associative array type. |
const object references cannot be reassigned. class Widget { int x; int y() const { return x; } }
const a = new Widget;
// Fine
a.y();
// error! can't modify const a
// a.x = 5;
// error! can't modify const a
// a = new Widget;
Rebindable!(Widget) does allow reassignment, while otherwise behaving exactly like a const Widget. class Widget { int x; int y() const { return x; } }
auto a = Rebindable!(const Widget)(new Widget);
// Fine
a.y();
// error! can't modify const a
// a.x = 5;
// Fine
a = new Widget;
Convenience function for creating a Rebindable using automatic type inference.
T obj
| A reference to an object, interface, associative array, or an array slice to initialize the Rebindable with. |
Rebindable initialized with the given reference.This function simply returns the Rebindable object passed in. It's useful in generic programming cases when a given object may be either a regular class or a Rebindable.
Rebindable!T obj
| An instance of Rebindable!T. |
obj without any modification.Similar to Rebindable!(T) but strips all qualifiers from the reference as opposed to just constness / immutability. Primary intended use case is with shared (having thread-local reference to shared class data)
| T | A class or interface type. |
class Data {}
static shared(Data) a;
static UnqualRef!(shared Data) b;
import core.thread;
auto thread = new core.thread.Thread({
a = new shared Data();
b = new shared Data();
});
thread.start();
thread.join();
assert(a !is null);
assert(b is null);
Order the provided members to minimize size while preserving alignment. Alignment is not always optimal for 80-bit reals, nor for structs declared as align(1).
| E | A list of the types to be aligned, representing fields of an aggregate such as a struct or class. |
char[][] names
| The names of the fields that are to be aligned. |
struct or class.struct Banner {
mixin(alignForSize!(byte[6], double)(["name", "height"]));
}
Defines a value paired with a distinctive "null" state that denotes the absence of a value. If default constructed, a Nullable!T object starts in the null state. Assigning it renders it non-null. Calling nullify can nullify it again.
Practically Nullable!T stores a T and a bool.
struct CustomerRecord
{
string name;
string address;
int customerNum;
}
Nullable!CustomerRecord getByName(string name)
{
//A bunch of hairy stuff
return Nullable!CustomerRecord.init;
}
auto queryResult = getByName("Doe, John");
if (!queryResult.isNull)
{
//Process Mr. Doe's customer record
auto address = queryResult.address;
auto customerNum = queryResult.customerNum;
//Do some things with this customer's info
}
else
{
//Add the customer to the database
}
import std.exception : assertThrown; auto a = 42.nullable; assert(!a.isNull); writeln(a.get); // 42 a.nullify(); assert(a.isNull); assertThrown!Throwable(a.get);
Constructor initializing this with value.
T value
| The value to initialize this Nullable with. |
If they are both null, then they are equal. If one is null and the other is not, then they are not equal. If they are both non-null, then they are equal if their values are equal.
Nullable!int empty; Nullable!int a = 42; Nullable!int b = 42; Nullable!int c = 27; writeln(empty); // empty writeln(empty); // Nullable!int.init assert(empty != a); assert(empty != b); assert(empty != c); writeln(a); // b assert(a != c); assert(empty != 42); writeln(a); // 42 assert(c != 42);
Check if this is in the null state.
true iff this is in the null state, otherwise false.Nullable!int ni; assert(ni.isNull); ni = 0; assert(!ni.isNull);
Forces this to the null state.
Nullable!int ni = 0; assert(!ni.isNull); ni.nullify(); assert(ni.isNull);
Assigns value to the internally-held state. If the assignment succeeds, this becomes non-null.
T value
| A value of type T to assign to this Nullable. |
Nullable wraps a type that already has a null value (such as a pointer), then assigning the null value to this Nullable is no different than assigning any other value of type T, and the resulting code will look very strange. It is strongly recommended that this be avoided by instead using the version of Nullable that takes an additional nullValue template argument. //Passes Nullable!(int*) npi; assert(npi.isNull); //Passes?! npi = null; assert(!npi.isNull);
Gets the value. this must not be in the null state. This function is also called for the implicit conversion to T.
Nullable.import core.exception : AssertError; import std.exception : assertThrown, assertNotThrown; Nullable!int ni; int i = 42; //`get` is implicitly called. Will throw //an AssertError in non-release mode assertThrown!AssertError(i = ni); writeln(i); // 42 ni = 5; assertNotThrown!AssertError(i = ni); writeln(i); // 5
Just like Nullable!T, except that the null state is defined as a particular value. For example, Nullable!(uint, uint.max) is an uint that sets aside the value uint.max to denote a null state. Nullable!(T, nullValue) is more storage-efficient than Nullable!T because it does not need to store an extra bool.
| T | The wrapped type for which Nullable provides a null value. |
| nullValue | The null value which denotes the null state of this Nullable. Must be of type T. |
Nullable!(size_t, size_t.max) indexOf(string[] haystack, string needle)
{
//Find the needle, returning -1 if not found
return Nullable!(size_t, size_t.max).init;
}
void sendLunchInvite(string name)
{
}
//It's safer than C...
auto coworkers = ["Jane", "Jim", "Marry", "Fred"];
auto pos = indexOf(coworkers, "Bob");
if (!pos.isNull)
{
//Send Bob an invitation to lunch
sendLunchInvite(coworkers[pos]);
}
else
{
//Bob not found; report the error
}
//And there's no overhead
static assert(Nullable!(size_t, size_t.max).sizeof == size_t.sizeof);
import std.exception : assertThrown; Nullable!(int, int.min) a; assert(a.isNull); assertThrown!Throwable(a.get); a = 5; assert(!a.isNull); writeln(a); // 5 static assert(a.sizeof == int.sizeof);
auto a = nullable!(int.min)(8); writeln(a); // 8 a.nullify(); assert(a.isNull);
Constructor initializing this with value.
T value
| The value to initialize this Nullable with. |
Check if this is in the null state.
true iff this is in the null state, otherwise false.Nullable!(int, -1) ni; //Initialized to "null" state assert(ni.isNull); ni = 0; assert(!ni.isNull);
Forces this to the null state.
Nullable!(int, -1) ni = 0; assert(!ni.isNull); ni = -1; assert(ni.isNull);
Assigns value to the internally-held state. If the assignment succeeds, this becomes non-null. No null checks are made. Note that the assignment may leave this in the null state.
T value
| A value of type T to assign to this Nullable. If it is nullvalue, then the internal state of this Nullable will be set to null. |
Nullable wraps a type that already has a null value (such as a pointer), and that null value is not given for nullValue, then assigning the null value to this Nullable is no different than assigning any other value of type T, and the resulting code will look very strange. It is strongly recommended that this be avoided by using T's "built in" null value for nullValue. //Passes enum nullVal = cast(int*) 0xCAFEBABE; Nullable!(int*, nullVal) npi; assert(npi.isNull); //Passes?! npi = null; assert(!npi.isNull);
Gets the value. this must not be in the null state. This function is also called for the implicit conversion to T.
Nullable.import std.exception : assertThrown, assertNotThrown; Nullable!(int, -1) ni; //`get` is implicitly called. Will throw //an error in non-release mode assertThrown!Throwable(ni == 0); ni = 0; assertNotThrown!Throwable(ni == 0);
Just like Nullable!T, except that the object refers to a value sitting elsewhere in memory. This makes assignments overwrite the initially assigned value. Internally NullableRef!T only stores a pointer to T (i.e., Nullable!T.sizeof == (T*).sizeof).
import std.exception : assertThrown; int x = 5, y = 7; auto a = nullableRef(&x); assert(!a.isNull); writeln(a); // 5 writeln(x); // 5 a = 42; writeln(x); // 42 assert(!a.isNull); writeln(a); // 42 a.nullify(); writeln(x); // 42 assert(a.isNull); assertThrown!Throwable(a.get); assertThrown!Throwable(a = 71); a.bind(&y); writeln(a); // 7 y = 135; writeln(a); // 135
Constructor binding this to value.
T* value
| The value to bind to. |
Binds the internal state to value.
T* value
| A pointer to a value of type T to bind this NullableRef to. |
NullableRef!int nr = new int(42); writeln(nr); // 42 int* n = new int(1); nr.bind(n); writeln(nr); // 1
Returns true if and only if this is in the null state.
true if this is in the null state, otherwise false.NullableRef!int nr; assert(nr.isNull); int* n = new int(42); nr.bind(n); assert(!nr.isNull && nr == 42);
Forces this to the null state.
NullableRef!int nr = new int(42); assert(!nr.isNull); nr.nullify(); assert(nr.isNull);
Assigns value to the internally-held state.
T value
| A value of type T to assign to this NullableRef. If the internal state of this NullableRef has not been initialized, an error will be thrown in non-release mode. |
import std.exception : assertThrown, assertNotThrown; NullableRef!int nr; assert(nr.isNull); assertThrown!Throwable(nr = 42); nr.bind(new int(0)); assert(!nr.isNull); assertNotThrown!Throwable(nr = 42); writeln(nr); // 42
Gets the value. this must not be in the null state. This function is also called for the implicit conversion to T.
import std.exception : assertThrown, assertNotThrown; NullableRef!int nr; //`get` is implicitly called. Will throw //an error in non-release mode assertThrown!Throwable(nr == 0); nr.bind(new int(0)); assertNotThrown!Throwable(nr == 0);
BlackHole!Base is a subclass of Base which automatically implements all abstract member functions in Base as do-nothing functions. Each auto-implemented function just returns the default value of the return type without doing anything.
The name came from Class::BlackHole Perl module by Sean M. Burke.
| Base | A non-final class for BlackHole to inherit from. |
AutoImplement, generateEmptyFunction
import std.math : isNaN;
static abstract class C
{
int m_value;
this(int v) { m_value = v; }
int value() @property { return m_value; }
abstract real realValue() @property;
abstract void doSomething();
}
auto c = new BlackHole!C(42);
writeln(c.value); // 42
// Returns real.init which is NaN
assert(c.realValue.isNaN);
// Abstract functions are implemented as do-nothing
c.doSomething();
WhiteHole!Base is a subclass of Base which automatically implements all abstract member functions as functions that always fail. These functions simply throw an Error and never return. Whitehole is useful for trapping the use of class member functions that haven't been implemented.
The name came from Class::WhiteHole Perl module by Michael G Schwern.
| Base | A non-final class for WhiteHole to inherit from. |
AutoImplement, generateAssertTrap
import std.exception : assertThrown;
static class C
{
abstract void notYetImplemented();
}
auto c = new WhiteHole!C;
assertThrown!NotImplementedError(c.notYetImplemented()); // throws an Error
AutoImplement automatically implements (by default) all abstract member functions in the class or interface Base in specified way.
The second version of AutoImplement automatically implements Interface, while deriving from BaseClass.
| how | template which specifies how functions will be implemented/overridden. Two arguments are passed to how: the type Base and an alias to an implemented function. Then how must return an implemented function body as a string. The generated function body can use these keywords:
// Prints log messages for each call to overridden functions.
string generateLogger(C, alias fun)() @property
{
import std.traits;
enum qname = C.stringof ~ "." ~ __traits(identifier, fun);
string stmt;
stmt ~= q{ struct Importer { import std.stdio; } };
stmt ~= `Importer.writeln("Log: ` ~ qname ~ `(", args, ")");`;
static if (!__traits(isAbstractFunction, fun))
{
static if (is(ReturnType!fun == void))
stmt ~= q{ parent(args); };
else
stmt ~= q{
auto r = parent(args);
Importer.writeln("--> ", r);
return r;
};
}
return stmt;
}
|
| what | template which determines what functions should be implemented/overridden. An argument is passed to what: an alias to a non-final member function in Base. Then what must return a boolean value. Return true to indicate that the passed function should be implemented/overridden. // Sees if fun returns something. enum bool hasValue(alias fun) = !is(ReturnType!(fun) == void); |
std.typecons module. Thus, any useful functions outside std.typecons cannot be used in the generated code. To workaround this problem, you may import necessary things in a local struct, as done in the generateLogger() template in the above example. parent keyword is actually a delegate to the super class' corresponding member function. [Bugzilla 2540] how and/or what may cause strange compile error. Use template tuple parameter instead to workaround this problem. [Bugzilla 4217] Predefined how-policies for AutoImplement. These templates are also used by BlackHole and WhiteHole, respectively.
Supports structural based typesafe conversion.
If Source has structural conformance with the interface Targets, wrap creates internal wrapper class which inherits Targets and wrap src object, then return it.
Extract object which wrapped by wrap.
interface Quack
{
int quack();
@property int height();
}
interface Flyer
{
@property int height();
}
class Duck : Quack
{
int quack() { return 1; }
@property int height() { return 10; }
}
class Human
{
int quack() { return 2; }
@property int height() { return 20; }
}
Duck d1 = new Duck();
Human h1 = new Human();
interface Refleshable
{
int reflesh();
}
// does not have structural conformance
static assert(!__traits(compiles, d1.wrap!Refleshable));
static assert(!__traits(compiles, h1.wrap!Refleshable));
// strict upcast
Quack qd = d1.wrap!Quack;
assert(qd is d1);
assert(qd.quack() == 1); // calls Duck.quack
// strict downcast
Duck d2 = qd.unwrap!Duck;
assert(d2 is d1);
// structural upcast
Quack qh = h1.wrap!Quack;
assert(qh.quack() == 2); // calls Human.quack
// structural downcast
Human h2 = qh.unwrap!Human;
assert(h2 is h1);
// structural upcast (two steps)
Quack qx = h1.wrap!Quack; // Human -> Quack
Flyer fx = qx.wrap!Flyer; // Quack -> Flyer
assert(fx.height == 20); // calls Human.height
// strucural downcast (two steps)
Quack qy = fx.unwrap!Quack; // Flyer -> Quack
Human hy = qy.unwrap!Human; // Quack -> Human
assert(hy is h1);
// strucural downcast (one step)
Human hz = fx.unwrap!Human; // Flyer -> Human
assert(hz is h1);
import std.traits : FunctionAttribute, functionAttributes;
interface A { int run(); }
interface B { int stop(); @property int status(); }
class X
{
int run() { return 1; }
int stop() { return 2; }
@property int status() { return 3; }
}
auto x = new X();
auto ab = x.wrap!(A, B);
A a = ab;
B b = ab;
writeln(a.run()); // 1
writeln(b.stop()); // 2
writeln(b.status); // 3
static assert(functionAttributes!(typeof(ab).status) & FunctionAttribute.property);
Options regarding auto-initialization of a RefCounted object (see the definition of RefCounted below).
Do not auto-initialize the object
Auto-initialize the object
Defines a reference-counted object containing a T value as payload.
An instance of RefCounted is a reference to a structure, which is referred to as the store, or storage implementation struct in this documentation. The store contains a reference count and the T payload. RefCounted uses malloc to allocate the store. As instances of RefCounted are copied or go out of scope, they will automatically increment or decrement the reference count. When the reference count goes down to zero, RefCounted will call destroy against the payload and call free to deallocate the store. If the T payload contains any references to GC-allocated memory, then RefCounted will add it to the GC memory that is scanned for pointers, and remove it from GC scanning before free is called on the store.
One important consequence of destroy is that it will call the destructor of the T payload. GC-managed references are not guaranteed to be valid during a destructor call, but other members of T, such as file handles or pointers to malloc memory, will still be valid during the destructor call. This allows the T to deallocate or clean up any non-GC resources immediately after the reference count has reached zero.
RefCounted is unsafe and should be used with care. No references to the payload should be escaped outside the RefCounted object.
The autoInit option makes the object ensure the store is automatically initialized. Leaving autoInit == RefCountedAutoInitialize.yes (the default option) is convenient but has the cost of a test whenever the payload is accessed. If autoInit == RefCountedAutoInitialize.no, user code must call either refCountedStore.isInitialized or refCountedStore.ensureInitialized before attempting to access the payload. Not doing so results in null pointer dereference.
// A pair of an `int` and a `size_t` - the latter being the // reference count - will be dynamically allocated auto rc1 = RefCounted!int(5); writeln(rc1); // 5 // No more allocation, add just one extra reference count auto rc2 = rc1; // Reference semantics rc2 = 42; writeln(rc1); // 42 // the pair will be freed when rc1 and rc2 go out of scope
RefCounted storage implementation.
Returns true if and only if the underlying store has been allocated and initialized.
Returns underlying reference count if it is allocated and initialized (a positive integer), and 0 otherwise.
Makes sure the payload was properly initialized. Such a call is typically inserted before using the payload.
Returns storage implementation struct.
Constructor that initializes the payload.
refCountedStore.isInitialized
Assignment operators
Returns a reference to the payload. If (autoInit == RefCountedAutoInitialize.yes), calls refCountedStore.ensureInitialized. Otherwise, just issues assert(refCountedStore.isInitialized). Used with alias refCountedPayload this;, so callers can just use the RefCounted object as a T.
The first overload exists only if autoInit == RefCountedAutoInitialize.yes. So if autoInit == RefCountedAutoInitialize.no or called for a constant or immutable object, then refCountedPayload will also be qualified as safe and nothrow (but will still assert if not initialized).
Initializes a RefCounted with val. The template parameter T of RefCounted is inferred from val. This function can be used to move non-copyable values to the heap. It also disables the autoInit option of RefCounted.
T val
| The value to be reference counted |
RefCounted containing val. static struct File
{
string name;
@disable this(this); // not copyable
~this() { name = null; }
}
auto file = File("name");
writeln(file.name); // "name"
// file cannot be copied and has unique ownership
static assert(!__traits(compiles, {auto file2 = file;}));
// make the file refcounted to share ownership
import std.algorithm.mutation : move;
auto rcFile = refCounted(move(file));
writeln(rcFile.name); // "name"
writeln(file.name); // null
auto rcFile2 = rcFile;
writeln(rcFile.refCountedStore.refCount); // 2
// file gets properly closed when last reference is dropped
Creates a proxy for the value a that will forward all operations while disabling implicit conversions. The aliased item a must be an lvalue. This is useful for creating a new type from the "base" type (though this is not a subtype-supertype relationship; the new type is not related to the old type in any way, by design).
The new type supports all operations that the underlying type does, including all operators such as +, --, <, [], etc.
| a | The value to act as a proxy for all operations. It must be an lvalue. |
struct MyInt
{
private int value;
mixin Proxy!value;
this(int n){ value = n; }
}
MyInt n = 10;
// Enable operations that original type has.
++n;
writeln(n); // 11
writeln(n * 2); // 22
void func(int n) { }
// Disable implicit conversions to original type.
//int x = n;
//func(n);
struct NewIntType
{
//Won't work; the literal '1'
//is an rvalue, not an lvalue
//mixin Proxy!1;
//Okay, n is an lvalue
int n;
mixin Proxy!n;
this(int n) { this.n = n; }
}
NewIntType nit = 0;
nit++;
writeln(nit); // 1
struct NewObjectType
{
Object obj;
//Ok, obj is an lvalue
mixin Proxy!obj;
this (Object o) { obj = o; }
}
NewObjectType not = new Object();
assert(__traits(compiles, not.toHash()));
import std.math;
float f = 1.0;
assert(!f.isInfinity);
struct NewFloat
{
float _;
mixin Proxy!_;
this(float f) { _ = f; }
}
NewFloat nf = 1.0f;
assert(!nf.isInfinity);
Typedef allows the creation of a unique type which is based on an existing type. Unlike the alias feature, Typedef ensures the two types are not considered as equals.
alias MyInt = Typedef!int;
static void takeInt(int) { }
static void takeMyInt(MyInt) { }
int i;
takeInt(i); // ok
takeMyInt(i); // fails
MyInt myInt;
takeInt(myInt); // fails
takeMyInt(myInt); // ok
| init | Optional initial value for the new type. For example: alias MyInt = Typedef!(int, 10); MyInt myInt; assert(myInt == 10); // default-initialized to 10 |
| cookie | Optional, used to create multiple unique types which are based on the same origin type T. For example: alias TypeInt1 = Typedef!int; alias TypeInt2 = Typedef!int; // The two Typedefs are the same type. static assert(is(TypeInt1 == TypeInt2)); alias MoneyEuros = Typedef!(float, float.init, "euros"); alias MoneyDollars = Typedef!(float, float.init, "dollars"); // The two Typedefs are _not_ the same type. static assert(!is(MoneyEuros == MoneyDollars)); |
Typedef type, you can use the TypedefType template to extract the type which the Typedef wraps.Get the underlying type which a Typedef wraps. If T is not a Typedef it will alias itself to T.
import std.typecons : Typedef, TypedefType; import std.conv : to; alias MyInt = Typedef!int; static assert(is(TypedefType!MyInt == int)); /// Instantiating with a non-Typedef will return that type static assert(is(TypedefType!int == int)); string num = "5"; // extract the needed type MyInt myInt = MyInt( num.to!(TypedefType!MyInt) ); writeln(myInt); // 5 // cast to the underlying type to get the value that's being wrapped int x = cast(TypedefType!MyInt) myInt; alias MyIntInit = Typedef!(int, 42); static assert(is(TypedefType!MyIntInit == int)); static assert(MyIntInit() == 42);
Allocates a class object right inside the current scope, therefore avoiding the overhead of new. This facility is unsafe; it is the responsibility of the user to not escape a reference to the object outside the scope.
The class destructor will be called when the result of scoped() is itself destroyed.
Scoped class instances can be embedded in a parent class or struct, just like a child struct instance. Scoped member variables must have type typeof(scoped!Class(args)), and be initialized with a call to scoped. See below for an example.
scoped object.class A
{
int x;
this() {x = 0;}
this(int i){x = i;}
~this() {}
}
// Standard usage, constructing A on the stack
auto a1 = scoped!A();
a1.x = 42;
// Result of `scoped` call implicitly converts to a class reference
A aRef = a1;
writeln(aRef.x); // 42
// Scoped destruction
{
auto a2 = scoped!A(1);
writeln(a2.x); // 1
aRef = a2;
// a2 is destroyed here, calling A's destructor
}
// aRef is now an invalid reference
// Here the temporary scoped A is immediately destroyed.
// This means the reference is then invalid.
version(Bug)
{
// Wrong, should use `auto`
A invalid = scoped!A();
}
// Restrictions
version(Bug)
{
import std.algorithm.mutation : move;
auto invalid = a1.move; // illegal, scoped objects can't be moved
}
static assert(!is(typeof({
auto e1 = a1; // illegal, scoped objects can't be copied
assert([a1][0].x == 42); // ditto
})));
static assert(!is(typeof({
alias ScopedObject = typeof(a1);
auto e2 = ScopedObject(); // illegal, must be built via scoped!A
auto e3 = ScopedObject(1); // ditto
})));
// Use with alias
alias makeScopedA = scoped!A;
auto a3 = makeScopedA();
auto a4 = makeScopedA(1);
// Use as member variable
struct B
{
typeof(scoped!A()) a; // note the trailing parentheses
this(int i)
{
// construct member
a = scoped!A(i);
}
}
// Stack-allocate
auto b1 = B(5);
aRef = b1.a;
writeln(aRef.x); // 5
destroy(b1); // calls A's destructor for b1.a
// aRef is now an invalid reference
// Heap-allocate
auto b2 = new B(6);
writeln(b2.a.x); // 6
destroy(*b2); // calls A's destructor for b2.a
Returns the scoped object.
Args args
| Arguments to pass to T's constructor. |
Defines a simple, self-documenting yes/no flag. This makes it easy for APIs to define functions accepting flags without resorting to bool, which is opaque in calls, and without needing to define an enumerated type separately. Using Flag!"Name" instead of bool makes the flag's meaning visible in calls. Each yes/no flag has its own type, which makes confusions and mix-ups impossible.
getLine (usually far away from its definition) can't be understood without looking at the documentation, even by users familiar with the API: string getLine(bool keepTerminator)
{
...
if (keepTerminator) ...
...
}
...
auto line = getLine(false);
Assuming the reverse meaning (i.e. "ignoreTerminator") and inserting the wrong code compiles and runs with erroneous results. After replacing the boolean parameter with an instantiation of Flag, code calling getLine can be easily read and understood even by people not fluent with the API: string getLine(Flag!"keepTerminator" keepTerminator)
{
...
if (keepTerminator) ...
...
}
...
auto line = getLine(Yes.keepTerminator);
The structs Yes and No are provided as shorthand for Flag!"Name".yes and Flag!"Name".no and are preferred for brevity and readability. These convenience structs mean it is usually unnecessary and counterproductive to create an alias of a Flag as a way of avoiding typing out the full type while specifying the affirmative or negative options. Passing categorical data by means of unstructured bool parameters is classified under "simple-data coupling" by Steve McConnell in the Code Complete book, along with three other kinds of coupling. The author argues citing several studies that coupling has a negative effect on code quality. Flag offers a simple structuring method for passing yes/no flags to APIs. When creating a value of type Flag!"Name", use Flag!"Name".no for the negative option. When using a value of type Flag!"Name", compare it against Flag!"Name".no or just false or 0.
When creating a value of type Flag!"Name", use Flag!"Name".yes for the affirmative option. When using a value of type Flag!"Name", compare it against Flag!"Name".yes.
Convenience names that allow using e.g. Yes.encryption instead of Flag!"encryption".yes and No.encryption instead of Flag!"encryption".no.
Flag!"abc" flag1;
writeln(flag1); // Flag!"abc".no
writeln(flag1); // No.abc
assert(!flag1);
if (flag1) assert(false);
flag1 = Yes.abc;
assert(flag1);
if (!flag1) assert(false);
if (flag1) {} else assert(false);
writeln(flag1); // Yes.abc
Detect whether an enum is of integral type and has only "flag" values (i.e. values with a bit count of exactly 1). Additionally, a zero value is allowed for compatibility with enums including a "None" value.
enum A
{
None,
A = 1 << 0,
B = 1 << 1,
C = 1 << 2,
D = 1 << 3,
}
static assert(isBitFlagEnum!A);
enum B
{
A,
B,
C,
D // D == 3
}
static assert(!isBitFlagEnum!B);
enum C: double
{
A = 1 << 0,
B = 1 << 1
}
static assert(!isBitFlagEnum!C);
A typesafe structure for storing combinations of enum values.
This template defines a simple struct to represent bitwise OR combinations of enum values. It can be used if all the enum values are integral constants with a bit count of at most 1, or if the unsafe parameter is explicitly set to Yes. This is much safer than using the enum itself to store the OR combination, which can produce surprising effects like this:
enum E
{
A = 1 << 0,
B = 1 << 1
}
E e = E.A | E.B;
// will throw SwitchError
final switch (e)
{
case E.A:
return;
case E.B:
return;
}
BitFlags can be manipulated with the usual operators import std.traits : EnumMembers;
// You can use such an enum with BitFlags straight away
enum Enum
{
None,
A = 1 << 0,
B = 1 << 1,
C = 1 << 2
}
BitFlags!Enum flags1;
assert(!(flags1 & (Enum.A | Enum.B | Enum.C)));
// You need to specify the `unsafe` parameter for enum with custom values
enum UnsafeEnum
{
A,
B,
C,
D = B|C
}
static assert(!__traits(compiles, { BitFlags!UnsafeEnum flags2; }));
BitFlags!(UnsafeEnum, Yes.unsafe) flags3;
immutable BitFlags!Enum flags_empty;
// A default constructed BitFlags has no value set
assert(!(flags_empty & Enum.A) && !(flags_empty & Enum.B) && !(flags_empty & Enum.C));
// Value can be set with the | operator
immutable BitFlags!Enum flags_A = flags_empty | Enum.A;
// And tested with the & operator
assert(flags_A & Enum.A);
// Which commutes
assert(Enum.A & flags_A);
// BitFlags can be variadically initialized
immutable BitFlags!Enum flags_AB = BitFlags!Enum(Enum.A, Enum.B);
assert((flags_AB & Enum.A) && (flags_AB & Enum.B) && !(flags_AB & Enum.C));
// Use the ~ operator for subtracting flags
immutable BitFlags!Enum flags_B = flags_AB & ~BitFlags!Enum(Enum.A);
assert(!(flags_B & Enum.A) && (flags_B & Enum.B) && !(flags_B & Enum.C));
// You can use the EnumMembers template to set all flags
immutable BitFlags!Enum flags_all = EnumMembers!Enum;
// use & between BitFlags for intersection
immutable BitFlags!Enum flags_BC = BitFlags!Enum(Enum.B, Enum.C);
writeln(flags_B); // (flags_BC & flags_AB)
// All the binary operators work in their assignment version
BitFlags!Enum temp = flags_empty;
temp |= flags_AB;
writeln(temp); // (flags_empty | flags_AB)
temp = flags_empty;
temp |= Enum.B;
writeln(temp); // (flags_empty | Enum.B)
temp = flags_empty;
temp &= flags_AB;
writeln(temp); // (flags_empty & flags_AB)
temp = flags_empty;
temp &= Enum.A;
writeln(temp); // (flags_empty & Enum.A)
// BitFlags with no value set evaluate to false
assert(!flags_empty);
// BitFlags with at least one value set evaluate to true
assert(flags_A);
// This can be useful to check intersection between BitFlags
assert(flags_A & flags_AB);
assert(flags_AB & Enum.A);
// Finally, you can of course get you raw value out of flags
auto value = cast(int) flags_A;
writeln(value); // Enum.A
Replaces all occurrences of From into To, in one or more types T. For example, ReplaceType!(int, uint, Tuple!(int, float)[string]) yields Tuple!(uint, float)[string]. The types in which replacement is performed may be arbitrarily complex, including qualifiers, built-in type constructors (pointers, arrays, associative arrays, functions, and delegates), and template instantiations; replacement proceeds transitively through the type definition. However, member types in structs or classes are not replaced because there are no ways to express the types resulting after replacement.
This is an advanced type manipulation necessary e.g. for replacing the placeholder type This in std.variant.Algebraic.
ReplaceType aliases itself to the type(s) that result after replacement.static assert(
is(ReplaceType!(int, string, int[]) == string[]) &&
is(ReplaceType!(int, string, int[int]) == string[string]) &&
is(ReplaceType!(int, string, const(int)[]) == const(string)[]) &&
is(ReplaceType!(int, string, Tuple!(int[], float))
== Tuple!(string[], float))
);
Ternary type with three truth values:
Ternary.yes for true
Ternary.no for false
Ternary.unknown as an unknown stateTernary a; writeln(a); // Ternary.unknown writeln(~Ternary.yes); // Ternary.no writeln(~Ternary.no); // Ternary.yes writeln(~Ternary.unknown); // Ternary.unknown
The possible states of the Ternary
Construct and assign from a bool, receiving no for false and yes for true.
Construct a ternary value from another ternary value
a | b | ˜a | a | b | a & b | a ^ b |
|---|---|---|---|---|---|
no | no | yes | no | no | no |
no | yes | yes | no | yes |
|
no | unknown | unknown | no | unknown |
|
yes | no | no | yes | no | yes |
yes | yes | yes | yes | no |
|
yes | unknown | yes | unknown | unknown |
|
unknown | no | unknown | unknown | no | unknown |
unknown | yes | yes | unknown | unknown |
|
unknown | unknown | unknown | unknown | unknown |
© 1999–2017 The D Language Foundation
Licensed under the Boost License 1.0.
https://dlang.org/phobos/std_typecons.html