std/result

module result for Result<T, E>

The ways out of a Result<T, E>, in the prelude, each stating what a failure gives. A result is ok(v) or err(e). There is no unwrap. map over a result is the core's step applied to the value of a success: ok(3) | map(n => n + 1) is ok(4).

• is_ok — Whether self is a success: ok(4) | is_ok is true.
• is_err — Whether self is a failure: err("x") | is_err is true.
• ok — The value of self when a success, and none when a failure: err("x") | ok is none.
• err — The error of self when a failure, and none when a success: ok(4) | err is none.
• unwrap_or — The value of self when a success, and default when a failure: err("x") | unwrap_or(0) is 0.
• unwrap_or_else — The value of self when a success, and default applied to the error when a failure: err("ab") | unwrap_or_else(e => e.size()) is 2.
• map_err — A failure with by applied to its error; a success is kept as it is: err("x") | map_err(e => e.upper()) is err("X").
• and_then — by applied to the value of a success, its own failure kept; a failure is kept as it is: ok(4) | and_then(n => ok(n * 2)) is ok(8).
• or_else — by applied to the error of a failure, giving another result; a success is kept as it is: err("x") | or_else(e => ok(e.size())) is ok(1).