Issue 9136 - Add isNested trait for aggregates and functions

[ghost]

http://d.puremagic.com/issues/show_bug.cgi?id=9136

This adds a new trait: __traits(isNested, T), which is true for type T if it's a nested type which holds a context pointer (aggregate or function).

Current library workarounds require using .stringof tricks, which probably isn't very reliable. This pull simplifies implementation of Phobos Pull 948.

I'll add a documentation pull if & after this pull is merged.

[alexrp]

Seems reasonable to me.

[ghost]

@9rnsr: If you find any gotchas -- it would be great to know so we can make this trait reliable from the get-go.

[9rnsr]

All test codes for __traits is in test/runnable/traits.d, so I recommend to collect into there.

[9rnsr]

LGTM.

[9rnsr]

@AndrejMitrovic: Indeed. For nested class type, checking isNested traits is fairly difficult.

[ghost]

All test codes for __traits is in test/runnable/traits.d, so I recommend to collect into there.

Thanks, I was wondering where to put the testcase. Will update soon.

[ghost]

Note: I've changed the implementation (sorry to reviewer Kenji). It was necessary to disallow invalid argument count, and invalid checks like e.g. __traits(isNested, 123).

[ghost]

I've rebased this again, after the tester is green we should try merging it.

[MartinNowak]

LGTM, but I would prefer to see a merged spec update first.

[ghost]

I'll make the spec pull.

Also I'm going to add another test-case which was missed:

static class A { static class SC { } class NC { } }
static assert(!__traits(isNested, A));
static assert(!__traits(isNested, A.SC));
static assert(__traits(isNested, A.NC));

[MartinNowak]

Also I'm going to add another test-case which was missed:

So this already works for classes, great.

[denis-sh]

Updated std.traits.{isNested,hasNested} implementation in dlang/phobos#948.