The short answer is “no, I can’t think of any”. The longer answer
follows in the form of thinking out loud.
All callable objects in C++ respond to (). This includes function
objects, function pointers, and member function pointers.
All callable objects in Ruby repond to #call(). This includes Procs,
Methods, Continuations, and other objects. Many callable objects also
respond to # and #to_proc().
The same idioms apply in both cases; there is an object, and you want to
call it, but you don’t care what kind of object it is. In C++ you use
(), and in Ruby you use #call().
I can imagine one other situation in C++:
#include
struct Foo
{
void foo() { std::cout << “Foo::Foo()” << std::endl; }
};
struct Bar
{
struct Boo
{
void operator()() { std::cout << “Bar::Boo::operator()” << std::endl; }
};
Boo foo;
};
template
void foo(T t)
{
t.foo();
}
int main()
{
Foo f; foo(f);
Bar b; foo(b);
}
Here Foo and Bar both act like they have a member function foo(), but in
the case of Bar, it’s just a function object that responds to ().
With a little bit of black magic, I can do this in Ruby without
overloading ():
class Foo
def foo; puts “Foo#foo”; end
end
class Bar
class Boo
def call; puts “Bar::Boo#call”; end
end
def initialize
@b = Boo.new
p = proc { @b.call() }
m = Module.new
m.instance_eval do
define_method(:foo, p)
end
self.extend(m)
end
end
def foo(t)
t.foo()
end
f = Foo.new; foo(f)
b = Bar.new; foo(b)
It’s all a matter of creating an object that responds to the agreed-upon
protocol. C++ needs to be able to overload () for
backward-compatibility with C, because function pointers are not
first-class objects and can’t have member functions. In Ruby there is
no such requirement.
Paul
···
On Fri, Aug 15, 2003 at 08:21:25PM +0900, Jim Weirich wrote:
But … I’m wondering.
Is there some idiom that would be facilitated by overloading ()? The
only thing I can think of are C++ templates where the same bit of code
might cause f in “f()” to be bound to a function name at one invocation
or a functor object in another. Since Ruby doesn’t have C++ like
templates, this isn’t an issue.
I can’t think of other useful scenarios, but then I’m probably
insufficiently imaginative.
I’d still like to