Extension methods and properties

[Chuck.Esterbrook]

Support extension methods and properties on existing classes, interfaces and structs whether they come from DLLs or declarations.

This feature is found in Smalltalk, Objective-C (categories), C#, VB and others. C# and VB do it on .NET 3.5, but Cobra is still targeting 2.0 and will support it there. The syntax will be:

extend Foo

def bar

pass

get baz as int

return 1

One interesting question is whether or not to allow a nil receiver. C# does which, imo, is quite strange. For "obj.Foo()" in C# you need to know if Foo() is declared in obj's type or outside of it to know whether or not you can pass nil.

[Chuck]

This was partially done in  Cobra 0.8.

[Chuck]

Change to enhancement.

[Chuck]

AFAIK what's missing is:

• Extensions X method overloads
• Extensions on generics

Other mind-benders may include:

• Extensions on method overloads in a generic type
• Generic extension methods (not to be confused with non-generic extension methods on generic types)
• Generic extension methods on method overloads in a generic type

Also of note, it's no longer clear whether or not extension properties are desirable. Cobra already allows "obj.foo" for invoking a method with no args, and it's not as if property-centric classes such as DataGridView are going to pick up on extension properties.

[Chuck]

Here is code for an extended, overloaded method:

extend String

	def split(chars as IList<of char>) as String[]
		return String[](5) # TODO
		

class X

	def main is shared
		s = 'a,b:c:d,e,f'
		trace s.split([c',', c':'])

This fails during code generation. But it may be failing due to a bug in _bindImp.

[Chuck]

Also, support shared extension methods:

extend String
    def foo is shared
        pass
# ...
    String.foo

[Chuck]

• Method overloads in extensions were done some time ago.
• Generics were done today in changeset:1853

There is still more testing and investigation to be done before this ticket can be closed. Please report any problems here or in the discussion forums.

[gauthier]

well done for shared extension methods :)

I think support for c# 3 extension methods is a must-have for next milestone (if I'm right, it's simple static method with an attribute for the first parameter), this would also bring nearer the linq goodness with IEnumerable...

[Chuck]

It's true we need to support C# 3 extension methods at some point, but currently we're on .NET 2.0 and I don't think we would see such things unless we moved to .NET 3.5. So I think before that we need to get a cobra-n20.exe and cobra-n35.exe going. Make sense?