Don't you need them anytime you have a struct with borrowed members? Even it just has a Cow you need the lifetime in the struct definition. Sometimes, but not a

Don't you need them anytime you have a struct with borrowed members? Even it just has a Cow you need the lifetime in the struct definition. Sometimes, but not always, you can elide the lifetimes in a function (iirc they have to occur at the outermost layer). But I definitely wouldn't call it unusual.