Understanding Rust Error E0088: Wrong Number of Lifetime Arguments

Demystifying Rust Error E0088

Rust Error E0088 occurs when a function or method call includes an incorrect number of lifetime arguments. In most cases, this error can be resolved by properly specifying the correct number of lifetime arguments or by letting the Rust compiler infer the lifetimes.

Example of Rust Error E0088

Consider the following erroneous code example that triggers Rust Error E0088:

fn f() {}

fn main() {
    f::<'static>() // error: wrong number of lifetime arguments: expected 0, found 1
}

In this example, the function f does not specify any lifetime arguments. However, when calling the function in the main function, a 'static lifetime argument is provided. This mismatch in the number of expected and actual lifetime arguments results in Rust Error E0088.

Resolving Rust Error E0088

To resolve Rust Error E0088, ensure that the function or method call and its definition have the correct number of lifetime arguments. In the case of the above example, we can fix the error by removing the unnecessary lifetime argument from the function call, like this:

fn f() {}

fn main() {
    f() // ok!
}

Compiler Lifetime Inference

It's essential to note that the Rust compiler can generally infer the lifetimes without explicit annotations. Consider the following example with and without lifetime annotations:

struct Foo {
    value: String
}

impl Foo {
    // with lifetime annotation
    fn get_value<'a>(&'a self) -> &'a str { &self.value }
    // without lifetime annotation, compiler can infer
    fn without_lifetime(&self) -> &str { &self.value }
}

fn main() {
    let f = Foo { value: "hello".to_owned() };

    println!("{}", f.get_value());
    println!("{}", f.without_lifetime());
}

Both methods, get_value and without_lifetime, are valid and equivalent. The Rust compiler is capable of inferring the lifetimes in the latter case without the need for explicit lifetime annotations.