Allow parameterless (except this parameter) extension methods to behave as properties to participate in pattern matching

[kyoyama-kazusa]

For example, consider the code:

// To check whether the value is power of two.
// This is an extension method of type 'System.Int32'.
public static bool IsPowerOfTwo(this int @this) => @this != 0 && (@this & (@this - 1)) == 0;

In this way, it's unnecessary to create a new syntax to describe so-called "extension properties". We use the parameterless extension methods for two purposes:

1. To describe them as normal methods that is just like the members belonging to certain types.
2. To use them on pattern matching (duck types) like

// Here 'variable' may be other types. (How about 'System.Object'?)
if (variable is int { IsPowerOfTwo: true } v)
{
    // Code using 'v'.
}

Thanks!

[alrz]

See #1047. it will enable this one way or another, though the syntax or semantics is not finalized yet.

[kyoyama-kazusa]

Thank you for your reply. I've seen that issue. operator is is a extremely powerful syntax! But... I think that operator is is a little bit... weird? operator is can only make a specified value as the right (v is SomeMethodAndReturnsAResult()) rather than a pattern { Prop: ConstantValue } or a variable defination (v is int i) (Or maybe I miss the point).

Of course, we can now use is pattern to check whether the instance is the specified type and the specified value. However, if we create a user-defined operator is, will there be any effects to break the basic checking?