Bug 12031 – Possible dollar handling inconsistencies in std.typecons.Typedef array

I am not sure, but perhaps this code shows some inconsistencies: import std.typecons: Typedef; ubyte[4] foo1() { ubyte[25] a; return a[$ - 4 .. $]; // OK } ubyte[4] foo2() { Typedef!(ubyte[25]) a; return a[$ - 4 .. $]; // Error } ubyte[4] foo3() { Typedef!(ubyte[25]) a; return a[a.length - 4 .. a.length]; // Error } ubyte[4] foo4() { Typedef!(ubyte[25]) a; typeof(return) result; result[] = a[a.length - 4 .. a.length]; // OK return result; } void main() {} dmd 2.065beta gives: test.d(8): Error: undefined identifier __dollar test.d(8): Error: undefined identifier __dollar test.d(12): Error: cannot implicitly convert expression (a.opSlice(21u, 25u)) of type ubyte[] to ubyte[4]

The first issue is a Phobos bug: it just doesn't forward opDollar. The second seems like a DMD bug.

I've submitted a pull for the opDollar issue, so I'm going to change this to a DMD bug so that those folks can take a look at the other issue. https://github.com/D-Programming-Language/phobos/pull/1899

Commits pushed to master at https://github.com/D-Programming-Language/phobos https://github.com/D-Programming-Language/phobos/commit/27a6d57972ea14e0bd9383d1b9f9450cecce2107 Fix Issue 12031 (partial) - opDollar for Typedef!T Just forwarding the various kinds of `opDollar` in `Proxy!T`. Partially fixes bug 12031 -- I believe a dmd change is needed to completely fix it (separate to opDollar forwarding). https://github.com/D-Programming-Language/phobos/commit/ae9356537e8511dd6074207d4649c2c93f3d83c5 Merge pull request #1899 from Poita/bug12031 Fix Issue 12031 (partial) - opDollar for Typedef!T

Now the error messages become: test.d(8,13): Error: cannot implicitly convert expression (a.opSlice(__dollar - 4u, __dollar)) of type ubyte[] to ubyte[4] test.d(12,13): Error: cannot implicitly convert expression (a.opSlice(21u, 25u)) of type ubyte[] to ubyte[4]

This is not a compiler bug. The problem is that `std.typecons.TypeDef` uses an inner `std.typecons.Proxy` but as documented `Proxy` blocks implicit conversions. Now the big question is if it's an "invalid issue" (and maybe that "TypeDef" DDOC is incomplete then) or if "TypeDef" implementation is not correct.

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