to_stringer.go

import (
    "fmt"
    "reflect"
    "strings"
)

type ToStringer struct {
    pieces []string
}

func (t *ToStringer) Add(name string, toAdd interface{}) *ToStringer {
    if toAdd == nil {
        return t
    }
    typ := reflect.TypeOf(toAdd)
    val := reflect.ValueOf(toAdd)
    if typ.Kind() == reflect.Ptr {
        if val.IsNil() {
            return t
        }
        // dereference the pointer
        toAdd = reflect.Indirect(val).Interface()
    }

    switch toAdd := toAdd.(type) {
    case string:
        if toAdd != "" {
            t.addPiece(fmt.Sprintf("%s=%q", name, toAdd))
        }
    case int, int8, int32, int64, uint, uint8, uint16, uint32, uint64:
        t.addPiece(fmt.Sprintf("%s=%d", name, toAdd))
    case float32, float64:
        t.addPiece(fmt.Sprintf("%s=%0.2f", name, toAdd))
    default:
        t.addPiece(fmt.Sprintf("%s=%v", name, toAdd))
    }
    return t
}

func (t *ToStringer) addPiece(piece string) {
    if piece != "" {
        t.pieces = append(t.pieces, piece)
    }
}

func (t *ToStringer) ToString() string {
    return "[" + strings.Join(t.pieces, " ") + "]"
}