On: Error handling in Rust

[maxbrunsfeld]

From the left-hand side of the `=>` arrows in the `match` expression.

[msie → maxbrunsfeld]

I know that. Where do they come from before that?

[steveklabnik → msie]

    match number_str.parse::<i32>() {

This matches on the return value of parse, which is an Result<T>. It can have two values: Err(E), or Ok(T).

        Ok(n) => Ok(2 * n),

This line matches an Ok(T), and binds the value of type T to n, which can then be used on the right hand side.

        Err(err) => Err(err),

this line matches an Err(T), and binds the value of type T to err, which can be used on the right hand side.

The right hand sides re-wrap these values into another Result.

[phaylon → steveklabnik]

Nitpick: Result<T, E> instead of Result<T> assuming Result is std::result::Result.

[steveklabnik → phaylon]

Ahh yes, thank you.

[msie → steveklabnik]

Thanks!