[WIP]: Add overload proc macro for #[splat] function overloading

[Ajay-singh1]

This is a proof of concept for the overload! macro that makes #[splat]
easier to use for function overloading.

What it does

Turns this:

overload! {
    fn foo(x: i32) { println!("i32: {}", x); }
    fn foo(x: f64) { println!("f64: {}", x); }
}

Into this (generated automatically):

trait FooArgs: std::marker::Tuple {
    fn call(self);
}
impl FooArgs for (i32,) {
    fn call(self) { let x = self.0; println!("i32: {}", x); }
}
impl FooArgs for (f64,) {
    fn call(self) { let x = self.0; println!("f64: {}", x); }
}
fn foo<T: FooArgs>(#[splat] args: T) {
    args.call()
}

Current limitations

• Only handles 2 free functions (not methods)
• Only handles single argument
• No return values yet

Next steps

• Handle multiple arguments
• Handle return values
• Handle methods

[teor2345]

Looks like you need to edit the Cargo.toml files to fix these CI errors, do you want some help with that?

error: the #[proc_macro] attribute is only usable with crates of the proc-macro crate type

[lib]
proc-macro = true

https://doc.rust-lang.org/reference/procedural-macros.html#r-macro.proc.def

error[E0432]: unresolved import proc_macro
error[E0433]: cannot find module or crate syn in this scope
error[E0432]: unresolved import quote

The dependency versions are in the base Cargo.toml, then they can get inherited by this crate's Cargo.toml.

[Ajay-singh1]

I'll fix it thanks!

…

On Mon, 13 Jul, 2026, 9:12 am teor, ***@***.***> wrote: ***@***.**** commented on this pull request. Looks like you need to edit the Cargo.toml files to fix these CI errors, do you want some help with that? error: the #[proc_macro] attribute is only usable with crates of the proc-macro crate type [lib]proc-macro = true https://doc.rust-lang.org/reference/procedural-macros.html#r-macro.proc.def error[E0432]: unresolved import proc_macro error[E0433]: cannot find module or crate syn in this scope error[E0432]: unresolved import quote The dependency versions are in the base Cargo.toml <https://github.com/rustfoundation/overloading-macros/blob/d4e14c09ce980ee6946c47429ae3a94d93096198/Cargo.toml#L28>, then they can get inherited by this crate's Cargo.toml <https://github.com/rustfoundation/overloading-macros/blob/d4e14c09ce980ee6946c47429ae3a94d93096198/splat-overload/Cargo.toml#L15> . — Reply to this email directly, view it on GitHub <#5?email_source=notifications&email_token=AI7B2GH4CVFQZWZHJA2CUED5ERLCLA5CNFSNUABKM5UWIORPF5TWS5BNNB2WEL2QOVWGYUTFOF2WK43UKJSXM2LFO4XTINRYGE3DANBTHE4KM4TFMFZW63VGMFZXG2LHN2SWK5TFNZ2KYZTPN52GK4S7MNWGSY3L#pullrequestreview-4681604398>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AI7B2GDSECVSXZQNNTZIPLD5ERLCLAVCNFSNUABGKJSXA33TNF2G64TZHMYTEOJRGQ2TIMBUGM5US43TOVSTWNBYGY4DANBXGU4DNILWAI> . You are receiving this because you were assigned.Message ID: ***@***.***>

[teor2345]

Let's fix and merge what we have now, then open other PRs for further changes?

[teor2345]

Good idea, I should do this in the blog post examples as well

[teor2345]

Looks like there's trailing whitespace on a bunch of these lines, running cargo fmt --all should get rid of them and pass CI.