vendor/github.com/go-logr/logr/examples/tab_logger.go

package main

import (
	"os"
	"fmt"
	"text/tabwriter"

	"github.com/go-logr/logr"
)

// TabLogger is a sample logr.Logger that logs to stderr.
// It's terribly inefficient, and is *only* a basic example.
type TabLogger struct{
	name string
	keyValues map[string]interface{}

	writer *tabwriter.Writer
}

var _ logr.Logger = &TabLogger{}

func (l *TabLogger) Info(msg string, kvs ...interface{}) {
	fmt.Fprintf(l.writer, "%s\t%s\t", l.name, msg)
	for k, v := range l.keyValues {
		fmt.Fprintf(l.writer, "%s: %+v  ", k, v)
	}
	for i := 0; i < len(kvs); i += 2 {
		fmt.Fprintf(l.writer, "%s: %+v  ", kvs[i], kvs[i+1])
	}
	fmt.Fprintf(l.writer, "\n")
	l.writer.Flush()
}

func (_ *TabLogger) Enabled() bool {
	return true
}

func (l *TabLogger) Error(err error, msg string, kvs ...interface{}) {
	kvs = append(kvs, "error", err)
	l.Info(msg, kvs...)
}

func (l *TabLogger) V(_ int) logr.InfoLogger {
	return l
}

func (l *TabLogger) WithName(name string) logr.Logger {
	return &TabLogger{
		name: l.name+"."+name,
		keyValues: l.keyValues,
		writer: l.writer,
	}
}

func (l *TabLogger) WithValues(kvs ...interface{}) logr.Logger {
	newMap := make(map[string]interface{}, len(l.keyValues)+len(kvs)/2)
	for k, v := range l.keyValues {
		newMap[k] = v
	}
	for i := 0; i < len(kvs); i += 2 {
		newMap[kvs[i].(string)] = kvs[i+1]
	}
	return &TabLogger{
		name: l.name,
		keyValues: newMap,
		writer: l.writer,
	}
}

func NewTabLogger() logr.Logger {
	return &TabLogger{
		writer: tabwriter.NewWriter(os.Stderr, 40, 8, 2, '\t', 0),
	}
}