Answer by BurntSushi5 for How to create a Rust struct with string members?

If the string has to be owned by the struct, then you should use String. Alternatively, you could use an &str with a static lifetime (i.e., the lifetime of the program). For example:

struct Foo {    bar: String,    baz: &'static str,}fn main() {    let foo = Foo {        bar: "bar".to_string(),        baz: "baz",    };    println!("{}, {}", foo.bar, foo.baz);}

If the lifetime of the string is unknown, then you can parameterize Foo with a lifetime:

struct Foo<'a> {    baz: &'a str,}

See also:

• What are the differences between Rust's `String` and `str`?

If you're not sure whether the string will be owned or not (useful for avoiding allocations), then you can use borrow::Cow:

use std::borrow::Cow;struct Foo<'a> {    baz: Cow<'a, str>,}fn main() {    let foo1 = Foo {        baz: Cow::Borrowed("baz"),    };    let foo2 = Foo {        baz: Cow::Owned("baz".to_string()),    };    println!("{}, {}", foo1.baz, foo2.baz);}

Note that the Cow type is parameterized over a lifetime. The lifetime refers to the lifetime of the borrowed string (i.e., when it is a Borrowed). If you have a Cow, then you can use borrow and get a &'a str, with which you can do normal string operations without worrying about whether to allocate a new string or not. Typically, explicit calling of borrow isn't required because of deref coercions. Namely, Cow values will dereference to their borrowed form automatically, so &*val where val has type Cow<'a, str> will produce a &str.