From a9b96f6bd9afdba139fd53a7b50772b363471973 Mon Sep 17 00:00:00 2001 From: Manish Goregaokar Date: Thu, 28 Aug 2014 16:52:30 +0530 Subject: [PATCH] Create 0053-ident-macros.md --- active/0053-ident-macros.md | 51 +++++++++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) create mode 100644 active/0053-ident-macros.md diff --git a/active/0053-ident-macros.md b/active/0053-ident-macros.md new file mode 100644 index 00000000000..8fd5340d37e --- /dev/null +++ b/active/0053-ident-macros.md @@ -0,0 +1,51 @@ +- Start Date: 2014-08-28 +- RFC PR: (leave this empty) +- Rust Issue: (leave this empty) + +# Summary + +Macros which resolve to idents should be usable in all positions that expect idents, including function/struct/enum names in definitions, et cetera. +Currently they can only be used as variable names. + +# Motivation + +This will allow for creating better macros which resolve to functions. For example: + +``` +macro_rules! make_setter( + ( $attr:ident ) => ( + fn concat_idents!(set_,$attr) (&self) -> u32 { + self.$attr + } + ); +) +``` + +can be created to generate setters just by calling `make_setter(foo)` (which will create `set_foo()`) + + +Currently, using macros in this manner will lead to errors like + +``` +test.rs:1:17: 1:18 error: expected `(` but found `!` +test.rs:1 fn concat_idents!(Foo, Bar) () { + ^ +``` + +See also: https://github.com/rust-lang/rust/issues/13294 + +# Detailed design + +This will probably require converting [`ast::Ident`](http://doc.rust-lang.org/master/syntax/ast/struct.Ident.html) to an enum allowing for a `NamedIdent` vs `MacroIdent` duality. + +# Drawbacks + +None that I see + +# Alternatives + +Suggestions welcome + +# Unresolved questions + +I'm rather unsure about the implementation.