/// <summary>
/// Gets a read-only wrapper around this dictionary. If <paramref name="cache"/> is already a wrapper for this
/// dictionary returns that, otherwise creates a new wrapper, stores it in <paramref name="cache"/>, and returns
/// that.</summary>
public static ReadOnlyDictionary <TK, TV> AsReadOnly <TK, TV>(this IDictionary <TK, TV> dict, ref ReadOnlyDictionary <TK, TV> cache)
{
if (dict == null)
{
throw new ArgumentNullException(nameof(dict));
}
if (cache == null || !cache.IsWrapperFor(dict))
{
cache = new ReadOnlyDictionary <TK, TV>(dict);
}
return(cache);
}