#![feature(specialization)] #![feature(negative_impls)] // Negative impl for u32 cannot "specialize" the base impl. trait MyTrait {} impl MyTrait for T {} impl !MyTrait for u32 {} //~ ERROR E0751 // The second impl specializes the first, no error. trait MyTrait2 {} impl MyTrait2 for T {} impl MyTrait2 for u32 {} fn main() {}