I'm using stable Rust. I'd like to create a value that has these properties: It can be called with normal function call syntax. Its type can be named, so you can store it in an ordinary variable without impl syntax or generics. There are of course the Fn* traits, but they might never be stabilize…

[image] crawdad: Is there any workaround for stable users? Not that I know of. The foo(some_arg) syntax is rewritten to call the call() method from the relevant Fn trait, so unless you figure out some voodoo magic to generate a callable, nameable closure, it won't be possible.

[image] Michael-F-Bryan: some voodoo magic to generate a callable //github.com/dtolnay/case-studies/tree/master/callable-types Much fun, very UB :upside_down_face:

I knew there'd be something from dtolnay which addresses this!

There's RFC 2515 ( tracking issue ) but it isn't stable yet.

I didn't think of using Deref. That makes it pretty easy. No need for all that unsafe, you can just allocate instead! fn main() { let func: Functionish = make_func(); func(); } fn make_func() -> Functionish { Functionish { f: Box::new(|| println!("printing")), } } struct F…

Here's a way of doing it without heap-allocation (unfortunately, requires nightly): #![feature(unboxed_closures)] #![feature(fn_traits)] struct Foo; impl Fn<()> for Foo { extern "rust-call" fn call(&self, _args: ()) { println!("Call (Fn) for Foo"); } } impl FnMut<()> for Foo { …

[image] crawdad: I didn't think of using Deref . That makes it pretty easy. No need for all that unsafe, you can just allocate instead! Oh, if your struct has a field which is a closure, you can simply deref to it indeed! mod lib { pub struct FunctionIsh<ImplFn> { f: ImplFn, …

Callable struct on stable

help

H2CO3 January 26, 2021, 8:14pm 6

It seems to me you would be better off relaxing requirement 1 – you can still do everything by calling a regular method that you could do by relying on () sugar.

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Callable struct on stable

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