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I'm not too familiar with rust's syntax -- isn't `!` normally used after identifiers to indicate macro invocation? Or is it part of the identifier that happens

I'm not too familiar with rust's syntax -- isn't `!` normally used after identifiers to indicate macro invocation? Or is it part of the identifier that happens to name a macro? More accurately, when I have a function that returns `!`, is that `!` a special syntax construct at the parser level, a keyword, or a name from the prelude? Or is there some special zero-name macro that is invoked? Can I put a bang in my own type name? https://doc.rust-lang.org/reference/types/never.html https://doc.rust-lang.org/reference/types/never.html seems to answer the question "it's special" I guess the docs are: https://doc.rust-lang.org/std/primitive.never.html https://doc.rust-lang.org/std/primitive.never.html

DougBTX 6y ago
> isn't `!` normally used after identifiers to indicate macro invocation? I'm not sure where that's explicitly documented, but the docs for procedural macros call it the "macro invocation operator": https://doc.rust-lang.org/reference/procedural-macros.html#function-like-procedural-macros https://doc.rust-lang.org/reference/procedural-macros.html#f... > Also, I tried searching but I couldn't find an entry for `!` in the docs. Yeah, that's one reason I'd prefer that it had an explicit name, rather than a single character.
nicoburns 6y ago
A special syntax construct at the parser level I think. In fact currently the `-> !` syntax for functions is it's own special syntax distinct (although v. similar in meaning) from the `!` type. It's not a macro (macro invocations just use the same character), and you can't have a '!' in your own type names.
- Sharlin 6y ago
  Yeah, in current stable Rust `-> !` is just a syntactic construct. But it is being reified into a proper first-class type [1], indeed in nightly you've been able to use it in most type positions for a while already (I actually forgot that the "basic" implementation is not yet stable!) [1] https://github.com/rust-lang/rust/issues/35121 https://github.com/rust-lang/rust/issues/35121

DougBTX 6y ago

> isn't `!` normally used after identifiers to indicate macro invocation? I'm not sure where that's explicitly documented, but the docs for procedural macros call it the "macro invocation operator": https://doc.rust-lang.org/reference/procedural-macros.html#function-like-procedural-macros https://doc.rust-lang.org/reference/procedural-macros.html#f... > Also, I tried searching but I couldn't find an entry for `!` in the docs. Yeah, that's one reason I'd prefer that it had an explicit name, rather than a single character.

nicoburns 6y ago

A special syntax construct at the parser level I think. In fact currently the `-> !` syntax for functions is it's own special syntax distinct (although v. similar in meaning) from the `!` type. It's not a macro (macro invocations just use the same character), and you can't have a '!' in your own type names.

Sharlin 6y ago
Yeah, in current stable Rust `-> !` is just a syntactic construct. But it is being reified into a proper first-class type [1], indeed in nightly you've been able to use it in most type positions for a while already (I actually forgot that the "basic" implementation is not yet stable!) [1] https://github.com/rust-lang/rust/issues/35121 https://github.com/rust-lang/rust/issues/35121