Implement SliceConcatExt for any iterable of string slices, not just Slice and Vec

[BlacklightShining]

Currently, these work (they both return "foo foo foo", as you'd expect):

["foo"; 3].connect(" ")
vec!["foo"; 3].connect(" ")

But these do not:

// type `collections::linked_list::LinkedList<&str>` does not implement any method in scope named `connect`
LinkedList::from_iter(repeat("foo").take(3)).connect(" ")
// type `core::iter::Take<core::iter::Repeat<&str>>` does not implement any method in scope named `connect`
repeat("foo").take(3).connect(" ")

Might std::slice::SliceConcatExt, be implemented for collections of and iterators over &strs?

[bluss]

I think coherence should allow it. Note that the slice versions iterate twice, to calculate the needed allocation exactly before concat. The iterator version can't do that, so it will be less efficient that way.

[gkoz]

Note that the slice versions iterate twice, to calculate the needed allocation exactly before concat. The iterator version can't do that, so it will be less efficient that way.

This got me thinking: if the ability to iterate twice is sufficient, could the methods be bounded on Self: Clone? This should preserve the efficiency while relaxing the requirements.

A quick and dirty POC.

[Centril]

Triage: no movement.