Loosen

Declares a derive-like function attr macro which creates another wrap-like function with single tuple-loosened argument, retrieved from the former function.

Upon call, the loosened function propagates the call with the flattened input tuple as arguments to the original function.

Example

#[loose] 
fn fa(a: A, b: B) {}

// normal call
fa(A, B); 

// loose call
let args = (A, B);
fa_loose(args); 
// ie. instead of two arguments, 
// there is only a single tuple argument

// usage in mappings
(0..10)
  .map(|_| (A, B))
  .map(fa_loose)
  .collect::<Vec<_>>();

Note

This is a draft and is my first try on proc-macros. I suggested this as an rfc before realising a proc macro would suffice: https://github.com/rust-lang/rfcs/issues/2667