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: attributes.go
    path of file: ./repos/tegola/vendor/google.golang.org/grpc/attributes
    
    the code of the file until where you have to start completion: /*
 *
 * Copyright 2019 gRPC authors.
 *
 * Licensed under the 
    
func (a *Attributes) String() string {
	var sb strings.Builder
	sb.WriteString("{")
	first := true
	for k, v := range a.m {
		var key, val string
		if str, ok := k.(interface{ String() string }); ok {
			key = str.String()
		}
		if str, ok := v.(interface{ String() string }); ok {
			val = str.String()
		}
		if !first {
			sb.WriteString(", ")
		}
		sb.WriteString(fmt.Sprintf("%q: %q, ", key, val))
		first = false
	}
	sb.WriteString("}")
	return sb.String()
}