Have syntactic sugar for 'class' (+ 'struct') and 'unmanaged' extension methods

[john-h-k]

Restricting extension methods too a base, interface, or struct class can be done simply by (obviously) defining the this parameter as the proper base/interface or System.ValueType for structs. It is also possible to constrain extension methods too class and unmanaged via generics, as such:

public void Function<T>(this T obj) where T : unmanaged

I suggest that these function signatures below should be equivalent to their generic counterparts

Function(this struct obj);
equivalent to
Function<T>(this T obj) where T : struct;
and
Function(this System.ValueType obj);

For reference types

Function(this class obj);
equivalent to
Function<T>(this T obj) where T : class;

For unmanaged types, the same, just with the unmanaged keyword.

Why?

• A cleaner syntax that loses no information
• Easier to search for (simply searching for this [keyword] rather than a generic type constraint with regex to ignore the name and other parameters etc).
• Syntax fits alongside generic type constraint syntax
• Use of struct, while equal in length / complexity to ValueType signature, is arguably clearer
• Wouldn't require any CLR changes
• Limits the instance type information of an extension method to keywords in the first method, rather than spread across generic type constraints which potentially constrain other generic types

[HaloFour]

A cleaner syntax that loses no information

It loses the information that Function is a generic member with a generic arity of 1, which is critically important as that is a part of the member name and signature. This proposal doesn't suggest how to reconcile that with multiple parameters or even multiple generic type parameters.