[Issue 6187] New: compiler could use move semantics for appending temporaries to an array

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=6187

           Summary: compiler could use move semantics for appending
                    temporaries to an array
           Product: D
           Version: D2
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: schveiguy at yahoo.com


--- Comment #0 from Steven Schveighoffer <schveiguy at yahoo.com> 2011-06-21 04:52:58 PDT ---
Currently, the following code:

import std.stdio;

struct S
{
   int x;
   this(this) { writeln("postblit"); }
   ~this() { writeln("dtor"); }
}

void main()
{
   S[] arr;
   arr ~= S();
}

outputs:

postblit
dtor

But it could have move semantics.  However, the runtime function which appends
data does not know whether the given data to append is an rvalue or not.  For
example, the following cannot have move semantics:

S s;
s.x = 1;
arr ~= s;
writeln(s.x);

So the compiler must give an additional flag (or call a separate runtime
function) when appending an rvalue.  When the compiler does this, flip the bug
to a druntime bug and assign it to me, and I'll fix the runtime.

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