Discussion Thread: DIP 1040--Copying, Moving, and Forwarding--Community Review Round 1

[tsbockman]

On Friday, 12 March 2021 at 22:46:05 UTC, tsbockman wrote:
> As for the proposed move operator syntax - no, we do not 
> currently use that syntax for move operators. None of the 
> various methods of moving things call them:
> ...
> Even if I manually call S.opAssign, a copy is performed for the 
> parameter, so it's *really* not a move operator.

I accidentally left out assignment in my example, but that's OK 
because it requires a different example to demonstrate the copy 
problem:

////////////////////////////////////
struct S {
     int x;
     this(int x) @safe {
         this.x = x; }
     this(ref typeof(this) s) @safe {
         x = 0; }
     void opAssign(S s) @safe {
         x = -s.x; }
}

void main() @system {
     import std.stdio : writeln;
     import std.algorithm.mutation : move;

     S s = 1, t;
     t = s;
     writeln(t);
}
////////////////////////////////////

Output:

     S(0)

So, the opAssign does get called in that case, but it's not a 
move because the copy constructor gets called first.