[Issue 9528] std.array.appender can't append elements with const members

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=9528



--- Comment #3 from rswhite4 at googlemail.com 2013-03-10 05:38:51 PDT ---
(In reply to comment #2)
> The problem is that appender is making the double assuption that unqual implies
> assignability, and that copyiable implies assignability (empace ony requires
> copyability). Finally, it makes the wrong assumption that you can call opAssign
> on something that is not yet initialized (append makes raw allocations).
> Amongst a few other bugs mind you.
> 
> There is a lot of broken in appender that I've tried to fix before, but it is
> very tricky because:
> 1) It is a ritical function that is used for strings, and needs to support
> CTFE.
> 2) Anything that fixes emplace must not slow it down.
> 3) It should be calling emplace instead of opAssign but emplace is currently
> broken for exactly the same reasons!
> 
> I should maybe try to fix it in smaller incremental steps, but it is very hard
> to knowingly deliver code that you know is broken, and know how to fix.

Possible solution for this:

static if (__traits(compiles, { _data.arr.ptr[len] = cast(Unqual!T) item; })) {
    _data.arr.ptr[len] = cast(Unqual!T) item;
} else {
    memcpy(&_data.arr.ptr[len], cast(Unqual!(T)*) &item, T.sizeof);
}

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