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Common standard interfaces

Context

The Go standard library defines many useful interfaces. The most common are:

fmt.Stringer – types that can describe themselves as a string (String() string)
error – the built‑in error interface (Error() string)
io.Reader and io.Writer – for reading and writing byte streams
sort.Interface – for sorting custom collections

Example

Implement fmt.Stringer for a Person type.

Code example

package main

import "fmt"

type Person struct {
    Name string
    Age  int
}

func (p Person) String() string {
    return fmt.Sprintf("%s (%d years old)", p.Name, p.Age)
}

func main() {
    alice := Person{"Alice", 30}
    fmt.Println(alice) // fmt.Print uses String() automatically
}

Output

Alice (30 years old)

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