Or Pattern
It's a little verbose if any two cases have common data and the same code to handle them. For example, here is an enum RGB and a function get_green to get the green value from it.
The RGB and RGBA cases can be combined as well. In an or pattern, the sub-patterns can introduce new variables, but they must be of the same type and have the same name in all sub-patterns. This restriction allows us to handle them uniformly.
enum Color {
Blue
Red
Green
RGB(Int, Int, Int)
RGBA(Int, Int, Int, Int)
} derive(Show)
fn get_green(color : Color) -> Int {
match color {
Blue | Red => 0
Green => 255
RGB(_, g, _) | RGBA(_, g, _, _) => g
}
}
fn main {
println("The green part of Red is \{get_green(Red)}")
println("The green part of Green is \{get_green(Green)}")
println("The green part of Blue is \{get_green(Blue)}")
println("The green part of RGB(0,0,0) is \{get_green(RGB(0,0,0))}")
println("The green part of RGBA(50,5,0,6) is \{get_green(RGBA(50,5,0,6))}")
}