std/option

module option for Option<T>

The ways out of an Option<T>, in the prelude, each stating what absence gives. There is no unwrap. map and filter over an option are the core's steps applied to the present value. See Option: a value that may be missing.

• is_some — Whether self holds a value: some(3) | is_some is true.
• is_none — Whether self is none: [1, 2][5] | is_none is true.
• unwrap_or — The value of self when present, and default otherwise: [1, 2][5] | unwrap_or(0) is 0.
• unwrap_or_else — The value of self when present, and what default returns otherwise; default is called only when self is none: [1, 2][5] | unwrap_or_else(() => 7) is 7.
• and_then — by applied to the value of self when present, its own none kept, and none otherwise: [4][0] | and_then(x => [10][x]) is none.
• or_else — self when present, and the option default returns otherwise: [1][5] | or_else(() => [9][0]) is 9.
• alternative — self when present, and other otherwise: [1][5] | alternative([9][0]) is 9.