Bug 17415 – std.conv.emplace does not forward arguments correctly

import std.conv : emplace; struct S { @disable this(this); } class C { this(S) {} } void[__traits(classInstanceSize, C)] holder = 0; emplace!C(S.init); I'd expect that to compile, and move the initializer correctly. But it does not compile (static assert), because emplace() copies arguments around, instead of using something like std.functional.forward. However, the fix is not trivial, some of the Phobos code actually depends on this, whether intentionally or accidentally, I cannot tell.

Obviously, should be: emplace!C(holder, S.init);

I might be wrong, but since you are disabling the postblit wouldn't you want to define the class ctor as: class C { this(const ref S) { /* magic */ } }

S.init counts as an rvalue. We should treat it for all purposes the same as: struct S { S init(); ... } The way the value is produced does not entail a copy. Then the rvalue is moved into the constructor of C, so the code is legit.

Should be fixed by https://github.com/dlang/druntime/pull/3352 and https://github.com/dlang/phobos/pull/7745.

Works since v2.096.