Protocols and generics

A protocol names methods a type can implement. A generic bounded by it is compiled once per concrete type, so dispatch costs nothing at run time.

Protocols and bounds

protocol declares the methods. impl P for T supplies them for one type, including a built-in type such as Int64.

A generic function takes a bound: fn label<T: Show>(x: T). The compiler generates one label per concrete type and calls the implementation directly. There is no table and no dynamic lookup: the choice is made once, while compiling.

A protocol can also declare an associated type. Chapter 11 uses one: Fallible owes an Output, which is what ? hands back.

site/guide/protocols.vyrnBuilt

// A protocol names methods a type can implement. A generic bounded by it calls
// those methods, and the compiler picks the implementation while it compiles —
// one function per concrete type, no table lookup at run time.
import { joinWith } from "std/strings"

protocol Show {
    fn show(self) -> String
}

impl Show for Int64 {
    fn show(self) -> String {
        return self.toString()
    }
}

impl Show for Bool {
    fn show(self) -> String {
        if self {
            return "yes"
        }
        return "no"
    }
}

fn label<T: Show>(x: T) -> String {
    return "[" + x.show() + "]"
}

export fn demo() -> String {
    return joinWith([label(41), label(true)], "\n")
}

fn main() -> Int64 {
    print(demo())
    return 0
}

// A protocol names methods a type can implement. A generic bounded by it calls
// those methods, and the compiler picks the implementation while it compiles —
// one function per concrete type, no table lookup at run time.
import { joinWith } from "std/strings"

protocol Show {
    fn show(self) -> String
}

impl Show for Int64 {
    fn show(self) -> String {
        return self.toString()
    }
}

impl Show for Bool {
    fn show(self) -> String {
        if self {
            return "yes"
        }
        return "no"
    }
}

fn label<T: Show>(x: T) -> String {
    return "[" + x.show() + "]"
}

export fn demo() -> String {
    return joinWith([label(41), label(true)], "\n")
}

fn main() -> Int64 {
    print(demo())
    return 0
}

[41] [yes]