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: cond.go
    path of file: ./repos/devspace/vendor/golang.org/x/text/runes
    
    the code of the file until where you have to start completion: // Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package runes

import (
	"unicode/utf8"

	"golang.org/x/text/transform"
)

// Note: below we pass invalid UTF-8 to the tIn and tNotIn transformers as is.
// This is done for various reasons:
// - To retain the semantics of the Nop transformer: if input is passed to a Nop
//   one would expect it to be unchanged.
//
    
func If(s Set, tIn, tNotIn transform.Transformer) Transformer {
	if tIn == nil && tNotIn == nil {
		return Transformer{transform.Nop}
	}
	if tIn == nil {
		tIn = transform.Nop
	}
	if tNotIn == nil {
		tNotIn = transform.Nop
	}
	sIn, ok := tIn.(transform.SpanningTransformer)
	if !ok {
		sIn = dummySpan{tIn}
	}
	sNotIn, ok := tNotIn.(transform.SpanningTransformer)
	if !ok {
		sNotIn = dummySpan{tNotIn}
	}

	a := &cond{
		tIn:    sIn,
		tNotIn: sNotIn,
		f:      s.Contains,
	}
	a.Reset()
	return Transformer{a}
}