Generics in Go

Type parameters and constraint interfaces.

type Number interface {
    ~int | ~int64 | ~float64
}

func Sum[T Number](items []T) T {
    var total T
    for _, item := range items {
        total += item
    }
    return total
}

func Map[T, U any](items []T, f func(T) U) []U {
    out := make([]U, 0, len(items))
    for _, item := range items {
        out = append(out, f(item))
    }
    return out
}

How it works

1. A constraint interface unions the allowed types.
2. ~int includes types whose underlying type is int.
3. Map[T, U any] transforms between element types.

Keywords and builtins used here

• any
• append
• float64
• for
• func
• int
• int64
• interface
• len
• make
• range
• return
• type
• var

The run, in numbers

Lines

19

Characters to type

310

Tokens

108

Three-star pace

110 tpm

At the three-star pace of 110 tokens a minute, this run takes about 59 seconds.

Type this snippet

Step 1 of 4 in Generics, step 13 of 19 in Interfaces & generics.

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Generics in other languages

• TypeScript