only require Show for elements joined with connect

Issue by panzi
Saturday May 03, 2014 at 02:19 GMT

For earlier discussion, see https://github.com/rust-lang/rust/issues/13911

This issue was labelled with: in the Rust repository

In most high level languages it's easy to turn a list/array of things into a comma separated string. In Rust there is the connect method, but it requires the elements to implement the trait std::str::Str. I would like this method to require std::fmt::Show instead. Alternatively a join method with according semantics that requires std::fmt::Show would suffice.

Currently you have to write:

let xs = [1, 2, 3];
let str_xs: ~[~str] = xs.iter().map(|x| x.to_str()).collect();
println!("xs = {}", str_xs.connect(", "));

let mut ys = Vec::new();
ys.push(4);
ys.push(5);
ys.push(6);
let str_ys: Vec<~str> = ys.iter().map(|y| y.to_str()).collect();
println!("ys = {}", str_ys.connect(", "));

This is pretty horrible. This would be much nicer:

let xs = [1, 2, 3];
println!("xs = {}", xs.connect(", "));

let mut ys = Vec::new();
ys.push(4);
ys.push(5);
ys.push(6);
println!("ys = {}", ys.connect(", "));

Start by reading the earlier discussion in rust-lang/rust#13911 and the surrounding RFC context. Investigate the existing connect API and the Str and Show traits in the Rust repository; done means the preferred API change is clearly specified and accepted for implementation.