nw, err := sw.WriteString(s[last:])
		n += nw
		if err != nil {
			return n, err
		}
	}
	return n, nil
}

// byteStringReplacer is the implementation that's used when all the
// "old" values are single ASCII bytes but the "new" values vary in size.
type byteStringReplacer struct {
	// replacements contains replacement byte slices indexed by old byte.
	// A nil []byte means that the old byte should not be replaced.

}

var algorithmTestCases = []struct {
	r    *Replacer
	want string
}{
	{capitalLetters, "*strings.byteReplacer"},
	{htmlEscaper, "*strings.byteStringReplacer"},
	{NewReplacer("12", "123"), "*strings.singleStringReplacer"},
	{NewReplacer("1", "12"), "*strings.byteStringReplacer"},
	{NewReplacer("", "X"), "*strings.genericReplacer"},
	{NewReplacer("a", "1", "b", "12", "cde", "123"), "*strings.genericReplacer"},
}