dup, idup, keys, values: if a type is known to have a postblit do not emit code for the non-postblit path and vice versa

[n8sh]

No description provided.

[dlang-bot]

Thanks for your pull request, @n8sh!

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	20741	enhancement	dup, idup for arrays plus keys, values for built-in associative arrays: if a type is known to have a postblit do not emit code for the non-postblit path and vice versa

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + druntime#3034"

[kinke]

Hmm, this doesn't seem to consider copy constructors at all. This should probably be refactored to use core.lifetime.emplace for copy-construction, which seems to correctly handle both cases:

import core.lifetime, core.stdc.stdio;

struct WithPostBlit
{
    int a = 42;
    this(int a) { this.a = a; }
    this(this) { printf("postblit: %d\n", a); }
}

struct WithCopyCtor
{
    int a = 42;
    this(int a) { this.a = a; }
    this(const ref WithCopyCtor rhs) { printf("copy ctor: %d => %d\n", a, rhs.a); }
}

void main()
{
    static void test(T)()
    {
    	T src = T(123);
        T dst = void;
        emplace(&dst, src);
    }

    test!WithPostBlit();
    test!WithCopyCtor();
}

=>

postblit: 123
copy ctor: 42 => 123

[n8sh]

That sounds right to me although making it work with keys and values would require more extensive changes since the arrays are built by the opaque functions rt.aaA._aaKeys and rt.aaA._aaValues which are non-templated and instead use TypeInfo. Touching up the arrays afterwards works for a postblit but not for a copy constructor.

Possible solutions:

• Expose the structure of built-in AAs so the object module can traverse them directly.
• Add a copyConstructor(void* src, void* dst) function to TypeInfo and change rt.aaA._aaKeys and rt.aaA._aaValues to call the copy constructor on their side.
• Add variants of rt.aaA._aaKeys and rt.aaA._aaValues that accept a copy constructor parameter and call it on their side.

[kinke]

Yeah I know that it's not directly related to this PR, it just stood out when looking at this code. There are surely more places where the copy ctor is ignored, incl. the compiler itself.

[thewilsonator]

grep -nrE "\<(for|foreach|foreach_reverse|if|while|switch|catch|version)\(" $(find src -name '*.d') ; test $? -eq 1
src/object.d:2535:    static if(__traits(hasPostblit, Value))
posix.mak:440: recipe for target 'style_lint' failed

-    static if(__traits(hasPostblit, Value))
+    static if (__traits(hasPostblit, Value))