Try It Yourself - SyntaxStudy Editor

HTML / CSS / JS

package main

import (
    "fmt"
    "io"
    "sort"
    "strings"
)

// Implement fmt.Stringer
type Celsius float64

func (c Celsius) String() string {
    return fmt.Sprintf("%.1f°C", float64(c))
}

// Custom error type (implements error interface)
type ValidationError struct {
    Field   string
    Message string
}

func (e *ValidationError) Error() string {
    return fmt.Sprintf("validation failed on %q: %s", e.Field, e.Message)
}

// Implement sort.Interface on a custom type
type ByLength []string

func (b ByLength) Len() int           { return len(b) }
func (b ByLength) Less(i, j int) bool { return len(b[i]) < len(b[j]) }
func (b ByLength) Swap(i, j int)      { b[i], b[j] = b[j], b[i] }

func main() {
    temp := Celsius(100)
    fmt.Println(temp) // uses String() automatically

err := &ValidationError{Field: "email", Message: "invalid format"}
    fmt.Println(err)

words := ByLength{"banana", "fig", "kiwi", "apple"}
    sort.Sort(words)
    fmt.Println(words)

// io.Reader / io.Writer composition
    r  := strings.NewReader("Hello, io interfaces!")
    var sb strings.Builder
    n, _ := io.Copy(&sb, r)
    fmt.Printf("copied %d bytes: %s
", n, sb.String())
}