You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: builder.go
    path of file: ./repos/rueidis/internal/cmds
    
    the code of the file until where you have to start completion: package cmds

import (
	"strings"
	"sync"
)

const ErrBuiltTwice = "a command should not be built twice"
const ErrUnfinished = "a command should be finished by calling Build() or Cache()"

var pool = &sync.Pool{New: fun
    
func (c Arbitrary) Keys(keys ...string) Arbitrary {
	if c.ks&NoSlot == NoSlot {
		for _, k := range keys {
			c.ks = NoSlot | slot(k)
			break
		}
	} else {
		for _, k := range keys {
			c.ks = check(c.ks, slot(k))
		}
	}
	c.cs.s = append(c.cs.s, keys...)
	return c
}