Similar to functions, implementations require care to remain generic.

#![allow(unused_variables)]
fn main() {
struct S; // Concrete type `S`
struct GenericVal<T>(T,); // Generic type `GenericVal`

// impl of GenericVal where we explicitly specify type parameters:
impl GenericVal<f32> {} // Specify `f32`
impl GenericVal<S> {} // Specify `S` as defined above

// `<T>` Must precede the type to remain generic
impl <T> GenericVal<T> {}
}

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functions returning references, impl, and struct