Bug 12223 – __traits(getMember,...) needed for aliases

Currently, "x.y" does two things: 1. Looks up "y" in the symbol scope of "x" 2. Interprets "y" with its "this" set to "x" Sometimes, it is useful to separate these two things. One can already do 1 without 2 using alias: alias y = x.y; However, there is no way to do 2 without 1. The closest thing we have is __traits(getMember, x, y) - however, it requires that y is a string, and does not work if it is an alias. Example: ////////////////////////////////// test.d ////////////////////////////////// static template T(alias v) { void set() { v = 42; } } struct S { int i; alias t = T!i; } void main() { alias f = S.t.set; // ... S s; // Goal: call f() with "this" set to s, like this: s.t.set(); // ... (but without referring to "t" or "set" directly) //s.f(); // NG //with (s) f(); // NG //struct W { S s; alias s this; alias wf = f; } //W w = W(s); w.wf(); // NG (Issue 12222) //__traits(getMember, s, f)(); // NG //__traits(getMember, // __traits(getMember, s, __traits(identifier, __traits(parent, f))), // __traits(identifier, f))(); // NG } //////////////////////////////////////////////////////////////////////////// I propose adding a __traits(child, x, y), since it will be the reverse operation of __traits(parent, y).

That's a rather complicated example. Is the following what you're after? ----- struct S { void foo() { } } void main() { alias f = S.foo; S s; __traits(getChild, s, f)(); // same as s.foo() } -----

Yes, but it should also work with the original example (if the child is an alias of a symbol that is not actually declared in the parent, but the "this" pointer of which is nevertheless of the type of the parent).

@rmanthorpe created dlang/dmd pull request #11442 "Issue 12223 - __traits(getMember,...) needed for aliases" mentioning this issue: - Issue 12223 - __traits(getMember,...) needed for aliases Add `__traits(child, p, c)` to interpret `c` with the `this` context set to `p`. This is the opposite of `__traits(parent, c)`. `c` should be a symbol mising it's `this` context, such an an alias to a member of `p`. https://github.com/dlang/dmd/pull/11442

dlang/dmd pull request #11442 "Fix Issue 12223 - __traits(getMember,...) needed for aliases" was merged into master: - da1a31509f43547a89fd7cd694499548ba345ee0 by Richard Manthorpe: Issue 12223 - __traits(getMember,...) needed for aliases Add `__traits(child, p, c)` to interpret `c` with the `this` context set to `p`. This is the opposite of `__traits(parent, c)`. `c` should be a symbol mising it's `this` context, such an an alias to a member of `p`. https://github.com/dlang/dmd/pull/11442

@ibuclaw created dlang/dmd pull request #12093 "[dmd-cxx] Backport more recent traits to the C++ port" mentioning this issue: - [dmd-cxx] Fix Issue 12223 - __traits(getMember,...) needed for aliases https://github.com/dlang/dmd/pull/12093

dlang/dmd pull request #12093 "[dmd-cxx] Backport more recent traits to the C++ port" was merged into dmd-cxx: - 1474ca231a6e9cf6a76c918661495242464b646e by Richard Manthorpe: [dmd-cxx] Fix Issue 12223 - __traits(getMember,...) needed for aliases https://github.com/dlang/dmd/pull/12093

This issue has been fixed by: https://github.com/dlang/dmd/pull/11442