This is a quick and silly syntax extension, mostly to familiarize myself with compiler plugins using custom attributes. It does the equivalent of Haskell's OverloadedStrings, i.e. it inserts an .into() call onto every string literal. No extra trait is necessary.

As a compiler plugin, requires nightly Rust. Add

#![feature(plugin)]
#![plugin(overload_strings)]

then apply the #[overload_strings] attribute on the item(s) you want to overload string literals in (module, fn, impl, ...).

The annotation does not automatically recurse into submodules, to keep surprises due to nonlocal effects down. It also ignores statics and consts, because they cannot contain method calls.

Where the ambiguity leads to errors in type inference, you can use the type_ascription nightly feature to disambiguate.

Now you can call functions expecting String, Cow<str>, and all other types that implement From<&str> with a string literal:

struct Person {
    first: String,
    last: String,
    birthplace: Cow<str>,
}

process_persons(&[
    Person { first: "Doug", last: "Piranha", birthplace: "London" },
    Person { first: "Dinsdale", last: "Piranha", birthplace: "London" },
]);