On 25 November 2012 23:31, Robert Haas <robertmhaas@gmail.com> wrote:
> The only other programming
> language I know of in which you can define what it means to cast
> between two data types is C++, and it's not generally considered one
> of that languages better features. AFAICT, they have implicit casts
> and explicit casts, but nothing intermediate.
Well, you can make your class copy-constructable by providing a
constructor (and a copy-assignment operator) whose only argument is,
say, an int. In additional to that, you could potentially define a
conversion operator, which will make the class implicitly cast back
into an int. That is kind of a big distinction, because it doesn't
have to go both ways, and in fact it usually doesn't - plenty of
working C++ programmers don't know what a conversion operator is, but
they could all tell you how to get this behaviour:
MyClass foo = 5; // actually calls copy constructor - equivalent to
MyClass foo(5);
foo = 4; // This calls copy assignment operator
--
Peter Geoghegan http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training and Services
