Why are explicit lifetimes needed in Rust?

Question

I was reading the lifetimes chapter of the Rust book, and I came across this example for a named/explicit lifetime:

struct Foo<\'a> {
    x: &\'a i         


        

Answer 1

The case from the book is very simple by design. The topic of lifetimes is deemed complex.

The compiler cannot easily infer the lifetime in a function with multiple arguments.

Also, my own optional crate has an OptionBool type with an as_slice method whose signature actually is:

fn as_slice(&self) -> &'static [bool] { ... }

There is absolutely no way the compiler could have figured that one out.