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Function std.algorithm.mutation.move

Moves source into target, via a destructive copy when necessary.

void move(T) (
  ref T source,
  ref T target
);

T move(T) (
  scope ref return T source
);

If T is a struct with a destructor or postblit defined, source is reset to its .init value after it is moved into target, otherwise it is left unchanged.

Preconditions

If source has internal pointers that point to itself and doesn't define opPostMove, it cannot be moved, and will trigger an assertion failure.

Parameters

NameDescription
source Data to copy.
target Where to copy into. The destructor, if any, is invoked before the copy is performed.

Example

For non-struct types, move just performs target = source: 

Object obj1 = new Object;
Object obj2 = obj1;
Object obj3;

move(obj2, obj3);
assert(obj3 is obj1);
// obj2 unchanged
assert(obj2 is obj1);

Example

// Structs without destructors are simply copied
struct S1
{
    int a = 1;
    int b = 2;
}
S1 s11 = { 10, 11 };
S1 s12;

move(s11, s12);

writeln(s12); // S1(10, 11)
writeln(s11); // s12

// But structs with destructors or postblits are reset to their .init value
// after copying to the target.
struct S2
{
    int a = 1;
    int b = 2;

    ~this() pure nothrow @safe @nogc { }
}
S2 s21 = { 3, 4 };
S2 s22;

move(s21, s22);

writeln(s21); // S2(1, 2)
writeln(s22); // S2(3, 4)

Example

Non-copyable structs can still be moved: 

struct S
{
    int a = 1;
    @disable this(this);
    ~this() pure nothrow @safe @nogc {}
}
S s1;
s1.a = 2;
S s2 = move(s1);
writeln(s1.a); // 1
writeln(s2.a); // 2

Example

opPostMove will be called if defined: 

struct S
{
    int a;
    void opPostMove(const ref S old)
    {
        writeln(a); // old.a
        a++;
    }
}
S s1;
s1.a = 41;
S s2 = move(s1);
writeln(s2.a); // 42

Authors

Andrei Alexandrescu

License

Boost License 1.0.