[Cython] pure mode quirk

[Stefan Behnel]

Hi,

when declaring a C function in pure mode, you eventually end up with this:

    @cython.cfunc
    @cython.returns(cython.bint)
    @cython.locals(a=cython.int, b=cython.int, c=cython.int)
    def c_compare(a,b):
        c = 5
        return a == b + c

That is very verbose, making it hard to find the name of the actual
function. It's also not very intuitive that @cython.locals() is the way to
declare arguments.

I would find it more readable to support this:

    @cython.cfunc(cython.bint, a=cython.int, b=cython.int)
    @cython.locals(c=cython.int)
    def c_compare(a,b):
        c = 5
        return a == b

But the problem here is that it conflicts with

    @cython.cfunc
    def c_compare(a,b):
        c = 5
        return a == b

when executed from Shadow.py. How should the fake decorator know that it is
being called with a type as first argument and not with the function it
decorates? Legacy, legacy ...

An alternative would be this:

    @cython.cfunc(a=cython.int, b=cython.int, _returns=cython.bint)
    @cython.locals(c=cython.int)
    def c_compare(a,b):
        c = 5
        return a == b

But that's not clearer than an explicit decorator for the return value.

I'm somewhat concerned about the redundancy this introduces with @locals(),
which could still be used to declare argument types (even conflicting
ones). However, getting rid of the need for a separate @returns() seems
worthwhile by itself, so this might provide a compromise:

    @cython.cfunc(returns=cython.bint)
    @cython.locals(a=cython.int, b=cython.int, c=cython.int)
    def c_compare(a,b):
        c = 5
        return a == b + c

This would work in Shadow.py because it's easy to distinguish between a
positional argument (the decorated function) and a keyword argument
("returns"). It might lead to bugs in user code, though, if they forget to
pass the return type as a keyword argument. Maybe just a minor concern,
because the decorator doesn't read well without the keyword.

What do you think? Is this worth doing something about at all?

Stefan