Support F#ish object expression or Java#ish anonymous clases

[dadhi]

• F#: https://docs.microsoft.com/en-us/dotnet/fsharp/language-reference/object-expressions#:~:text=An%20object%20expression%20is%20an,interface%2C%20or%20set%20of%20interfaces.
• Java: https://docs.oracle.com/javase/tutorial/java/javaOO/anonymousclasses.html

Basically I always wanted this for the in-place IDisposable implementation, but other things could be useful too, e.g. quick Stub implementations in tests:

bool disposed = false;
using var x = new IDisposable { public void Dispose() => disposed = true; };

var depCalled = false;
new Tested(new IDependency { public CalledByTested() => depCalled = true; });

[qwertie]

Hmm, this is the sort of thing that requires non-local transformation (as the usual in-place macro transformations are useless), and I have done these in the past with top-of-file macros like #useSymbols and #ecs that preprocess the entire file and then postprocesses it to make the requested transformation(s).

Edit: I wrote this response without noticing that it doesn't actually do what you wanted. You wanted to define a class inside a method that would edit a local variable of the same method. That's a tough requirement that I haven't attempted to fulfill.

The problem can be broken down into two independent macros. The first macro is a non-local transformation called outsideCurrentMethod:

    outsideCurrentMethod {
        // gee, this class is useless, but it's just an example
        class MyIDisposable : IDisposable {
            bool disposed = false;
            public void Dispose() => disposed = true;
        };
    }
    using var x = new MyIDisposable();

Its job would be to make move something from inside a method to outside a method (and there could be related macros like atNamespaceScope and atOuterScope).

The second macro would be a local transformation giving you what you actually want, an anonymous object. The syntax you suggested is not viable in EC#, but you could use a syntax like this:

    // Note 1: I changed your example to use conventional `using` syntax
    // Note 2: you should really just use on_finally for this sort of thing
    using (var x = anon_object(IDisposable) {
        // I'm assuming we'll make a reference the outer class available
        public void Dispose() => outer.disposed = true;
    }) {
        DoStuffWith(x);
    }

I'd like to see outsideCurrentMethod, atNamespaceScope, atOuterScope included as part of #ecs, but the second macro is something someone could implement themselves with help from outsideCurrentMethod:

#ecs;

define anon_object($(..bases), { $(..content); }) {
	#runSequence {
		outsideCurrentMethod {
			class InnerClassunique# : $bases {
				#outerTypeName outer;
				public InnerClassunique#(#outerTypeName outer) => this.outer = outer; //
								
				$content;
			}
		}
		new InnerClassunique#(this);
	}
}

using (var x = anon_object(IDisposable) { public void Dispose() => outer.disposed = true; }) 
	DoSomethingWith(x);

While trying this macro I ran into more bugs in #useSequenceExpressions, which I fixed. I also realized that it is necessary to know the name of the outer class - above I've pretended that there is another macro called #outerTypeName which reports this piece of information, but a simpler approach is to add another argument to anon_object to explicitly tell it the name of the outer class.

And of course one also needs a macro to transform outsideCurrentMethod.

Might you care to help out by attempting to write the latter macro? If so I can give you tips.

[dadhi]

@qwertie I need some time to process it.