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

I've found another great explanation here: http://doc.rust-lang.org/0.12.0/guide-lifetimes.html#returning-references.

In general, it is only possible to return references if they are derived from a parameter to the procedure. In that case, the pointer result will always have the same lifetime as one of the parameters; named lifetimes indicate which parameter that is.