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Generics

Wave generics are a feature for writing type-safe functions without code duplication.

Key Rules:

  • Type arguments must be explicitly specified.
  • Type inference is not allowed.

1. Declaration of Generic Functions​

fun identity<T>(x: T) -> T {
    return x;
}

Invocation:

fun main() {
    var a: i32 = identity<i32>(10);
    var b: f64 = identity<f64>(3.14);
}

2. Multiple Type Parameters​

struct Pair<A, B> {
    first: A;
    second: B;
}

fun pair<A, B>(a: A, b: B) -> Pair<A, B> {
    return Pair<A, B> {
        first: a;
        second: b;
    };
}

fun main() {
    var p: Pair<i32, f64> = pair<i32, f64>(1, 2.5);
}

3. Generic Structures​

struct Vec<T> {
    data: ptr<T>;
    len: i64;
}

fun main() {
    var v: Vec<i32>;
}

4. Nested Generics​

struct Vec<T> {
    data: ptr<T>;
    len: i64;
}

fun main() {
    var nested: Vec<Vec<i32>>;
}

5. Using with the Standard Library​

import("std::math::int");
import("std::env::environ");

fun main() {
    var x: i32 = num_abs<i32>(-100, 0);

    var r: EnvResult<i32> = env_get_i32("PORT");
    var port: i32 = env_unwrap_or<i32>(r, 8080);
}

Common Mistakes​

var x: i32 = identity(10); // Missing type argument (not allowed)

Must be called as follows.

var x: i32 = identity<i32>(10);