# Idea: elide parens/brackets on unparametrized macros **URL:** \ **Category:** language design\ **Created:** [January 10, 2018, 7:33pm UTC](https://internals.rust-lang.org/t/idea-elide-parens-brackets-on-unparametrized-macros/6527 "2018-01-10T19:33:40Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![mark-i-m](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/mark-i-m/32/3167_2.png) [@mark-i-m](https://internals.rust-lang.org/u/mark-i-m)\ **Post date:** [January 10, 2018, 7:33pm UTC](https://internals.rust-lang.org/t/idea-elide-parens-brackets-on-unparametrized-macros/6527/1 "2018-01-10T19:33:40Z")
Could we syntactically eliminate the `()`/`{}`/`[]` after “calling” an unparameterized macro? In other words: ```rust macro_rules! foo { () => { ... } } ``` could be invoked with `foo!` rather than `foo!()`. The motivation is primarily to avoid a paper cut. I can imagine a few use cases that would become more ergonomic: ```rust let my_vec = vec!; // vec![]` println!; // println!() ok! // Maybe shorthand for Ok(()) -- just an idea ? ``` I don’t see any obvious syntactic ambiguities that arise, and the change is purely syntactic, so the only part of the compiler that changes is the parser, I think. Any thoughts? ---
**Author:** ![bluss](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/bluss/32/2264_2.png) [@bluss](https://internals.rust-lang.org/u/bluss)\ **Post date:** [January 10, 2018, 8:06pm UTC](https://internals.rust-lang.org/t/idea-elide-parens-brackets-on-unparametrized-macros/6527/2 "2018-01-10T20:06:44Z")
macros without parameters rarely have very interesting effect, do they? It is unavoidably a knee-jerk reaction here, but I don’t think `vec!` is better than `vec![]` — then it even loses those brackets it has borrowed from the array or slice, to remind you of them. ---
**Author:** ![leonardo](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/leonardo/32/1344_2.png) [@leonardo](https://internals.rust-lang.org/u/leonardo)\ **Post date:** [January 10, 2018, 8:10pm UTC](https://internals.rust-lang.org/t/idea-elide-parens-brackets-on-unparametrized-macros/6527/3 "2018-01-10T20:10:49Z")
What I don’t like a lot is both versions being accepted: ``` fn main() { let v1: Vec = vec![]; let v2: Vec = vec!(); } ``` Often in programming languages I prefer the Python Zen “There should be one-- and preferably only one --obvious way to do it.”. ---
**Author:** ![mbrubeck](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/mbrubeck/32/174_2.png) [@mbrubeck](https://internals.rust-lang.org/u/mbrubeck)\ **Post date:** [January 10, 2018, 9:02pm UTC](https://internals.rust-lang.org/t/idea-elide-parens-brackets-on-unparametrized-macros/6527/4 "2018-01-10T21:02:26Z")
`unreachable!` seems like a good use case for this. Similarly, `unimplemented!` ---
**Author:** ![petrochenkov](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/petrochenkov/32/2784_2.png) [@petrochenkov](https://internals.rust-lang.org/u/petrochenkov)\ **Post date:** [January 10, 2018, 9:11pm UTC](https://internals.rust-lang.org/t/idea-elide-parens-brackets-on-unparametrized-macros/6527/5 "2018-01-10T21:11:45Z")
This looks kinda tempting. If macros with `()`/etc are “functions” and take arguments, then macros without `()` are “constants”. It would be nice to use them for macros that actually unwrap into constants, kinda like ```rust /* "Constant" macro */ #define CONST 10 /* "Function" macro */ #define FN(a, b, c) ((a) + (b) + (c)) ``` in C. I don’t think there are syntactic ambiguities or any similar technical problems, but I still have mixed feelings about the syntax, not sure why. ---
**Author:** ![withoutboats](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/withoutboats/32/4560_2.png) [@withoutboats](https://internals.rust-lang.org/u/withoutboats)\ **Post date:** [January 10, 2018, 9:59pm UTC](https://internals.rust-lang.org/t/idea-elide-parens-brackets-on-unparametrized-macros/6527/6 "2018-01-10T21:59:15Z")
I feel better about this for `panic!` variants than for `vec!`, but this seems like a very fuzzy feeling for which I don’t have a good justification. ---
**Author:** ![mark-i-m](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/mark-i-m/32/3167_2.png) [@mark-i-m](https://internals.rust-lang.org/u/mark-i-m)\ **Post date:** [January 10, 2018, 11:10pm UTC](https://internals.rust-lang.org/t/idea-elide-parens-brackets-on-unparametrized-macros/6527/7 "2018-01-10T23:10:49Z")
> [@petrochenkov](#): > > but I still have mixed feelings about the syntax, not sure why. > [@withoutboats](#): > > but this seems like a very fuzzy feeling for which I don’t have a good justification. TBH, I had the same hesitation. On introspection, here what I think I am feeling: Macros are great if you have some little piece of code that works the same way but with a few values changed. I don't think that macros should be used if other language constructs could be instead. Using a macro to insert _the same constant AST_ in multiple places feels in some way like a violation of that intuition. I would argue that this isn't a problem with this particular syntax though. Rather it's a choice of whether to use a macro at all for something. ---
**Author:** ![system](https://sea2.discourse-cdn.com/flex002/user_avatar/internals.rust-lang.org/system/32/14092_2.png) [@system](https://internals.rust-lang.org/u/system)\ **Post date:** [March 25, 2019, 8:29am UTC](https://internals.rust-lang.org/t/idea-elide-parens-brackets-on-unparametrized-macros/6527/8 "2019-03-25T08:29:30Z")
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