func (f *F) Get(key string) (interface{}, bool) {
	val, ok := f.nodes[key]
	if ok {
		return val, true
	}
	if f.parent != nil {
		return f.parent.Get(key)
	}
	return nil, false
}
Get returns the key from the fields in O(n), where n is the number of entries.
package log
import (
	"fmt"
)
var _ Fielder = &F{}
type Fielder interface {
	Fields() map[string]interface{}
}
func Fields(pairs ...interface{}) *F {
	return &F{
		nodes: pairsToMap(pairs...),
	}
}
type F struct {
	parent *F
	nodes  map[string]interface{}
}