Limit trait implementations to traits you own or types you own

[sezna]

I am not implementing this in the MVP, but to prevent random pollution of the method namespace of types when you import libraries, Rust prevents you from implementing a trait for a type when you don't own either the trait or the type. We should do this eventually.

[mohammadfawaz]

@sezna can you elaborate a bit on what exactly this means?

[sezna]

Here is a reproduction in Rust..

It is a safety measure to prevent dependencies from overriding traits on imported structs, which would be a big vulnerability. E.g.:

1. You import serde_json
2. You import foo
3. foo overwrites impl Serialize for String with its own implementation which also copies the contents of your home directory and sends them to a super secret black hat hacking organization

in the above scenario, you, the user, had no idea that Serialize was being overridden. That's why crates must introduce their own new wrapper traits, so additional functionality built on top of existing traits can remain opt-in.