Idea: Syntactic sugar for rust-style `impl` directive

Language Design
1

I’ve been finding myself writing “classes” using the using ... for ... global syntax, like so:

struct User {
    uint id;
    string username;
}

library UserLib {
    function displayName (User memory self) public {
        // ...
    }
}

using UserLib for User global;

This becomes very similar to rust-style classes:

struct User {
    id : u64,
    username : String
}

impl User {
    fn display_name(&self) -> String {
        return format!("@{} ({})", self.username, self.id).to_string();
    }
}

The syntactic sugar will be a new impl directive, which basically transpiles into library + using ... for. The following will be identical to the first snippet:

struct User {
    uint id;
    string username;
}

impl User {
    function displayName (User memory self) public {
        // ...
    }
}

One issue I can think of would be that it becomes impossible to import the library on its own.
A possible solution might be to expose some reflection api, e.g.: type(User).impl or something like that.

I also didn’t consider whether this would work for user-defined types.

Has something like this been considered already? I searched but couldn’t find anything.
WDYT?

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