On 03/18/2013 03:23 PM, Chris Angelico wrote:
The languages that permit you to assign to a function call all have
some notion of a reference type.
Assigning to function calls is orthogonal to reference types. For
example, Python manages assignment to subscripts without having
references just fine:
val = obj[index] # val = obj.__getitem__(index)
obj[index] = val # obj.__setitem__(index, val)
In analogy with that, Python could implement what looks like assignment
to function call like this:
val = f(arg) # val = f.__call__(arg)
f(arg) = val # f.__setcall__(arg, val)
I am not arguing that this should be added, I'm only pointing out that
Python's object customization is not fundamentally at odds with
assignment to function calls. Having said that, I am in fact arguing
that Python doesn't need them. All C++ uses of operator() overloads can
be implemented with the subscript operator.
Even if one needs more different assignments than there are operators,
Python can provide it as easily as C++. For example, on
std::vector::operator[] provides access to the container without error
checking, and std::vector::at() checks bounds:
vec[i] = val // no error checking
vec.at(i) = val // error checking
This is trivially translated to Python as:
vec[i] = val # primary functionality, use __setitem__
vec.at[i] = val # secondary functionality, __setitem__ on a proxy
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