cmp/report.go
func (r *defaultReporter) String() string {
	assert(r.root != nil && r.curr == nil)
	if r.root.NumDiff == 0 {
		return ""
	}
	return formatOptions{}.FormatDiff(r.root).String()
}
func (r *defaultReporter) String() string {
	assert(r.root != nil && r.curr == nil)
	if r.root.NumDiff == 0 {
		return ""
	}
	return formatOptions{}.FormatDiff(r.root).String()
}
// String provides a full report of the differences detected as a structured
// literal in pseudo-Go syntax. String may only be called after the entire tree
// has been traversed.