Operator overloading - Gpc

1 Apr 2003


      Up to now, GPC supports overloading of binary operators like `+' and
user-defined operators such as `Foo', but also only as binary
operators. I propose to extend and generalize this mechanism, e.g.
to unary operators.
Besides the usual unary operators like `+' and `-', you can define
your address operator as `@' (BP compatible) or `&' (like in C) or
whatever you prefer. Also other C operators like `++' can then be
easily defined without the need to have them built-in.
A special case would be the `^' operator since it's used both prefix
(in pointer type definitions) and postfix (in pointer dereferences).
I'm still thinking about the syntax for the operator declarations,
but `operator ^ (...)' and `^ operator (...)' would seem to be the
most obvious choices.
Some time ago, someone asked for backslash interpretation in string
literals. Redefining the `'' (i.e., single quote) operator would
make this easy. Also, the BP operators `#' and `^' (as in `^C') for
character constants could be defined in a similar way, without
messing up the syntax when they're built in.
The same applies to BP's `$' for hex integer constants. But, OTOH,
friends of the C syntax could define `0x' for hex and, if they like,
they could even define the `0' operator for octal constants.
Those who've always complained about Pascal's verbosity, could
finally define the `{' and `}' operators as `begin' and `end'
(preferably after defining the comment operator to `(*', `//' or
whatever they prefer). And those who would prefer `;' as a statment
terminator (as in C) instead of a statment separator can simply
redefine this operator.
Back to binary operators, apart from `:=' (as recently requested),
also `,' would be a very interesting one. We could have all the
interesting properties of this C operator in Pascal.
Overloading `[' (for self-made arrays) and `.' (for records/objects)
would work like in C++, of course, and can probably be used to
implement Delphi-compatible object properties without further
compiler support. Perhaps we can even define `class' as an operator
(that inherits from `object', and `^') to provide for classes with
implicit references.
The `_' operator could be defined to be rejected in identifiers in
classic Pascal (so we don't need the explicit compiler checks we
have now), whereas, e.g., international letters can be allowed in
identifiers by defining them as new operators.
Overloading the `if' operator could be useful to make a new
conditional syntax -- perhaps with `endif' to avoid problems with
dangling `else' etc.
By overloading `const' to `var' for typed arguments, BP's "typed
constants" could be supported without any contortions in the
compiler.
Finally, overloading the `operator' operator seems very interesting,
but I'll have to work out the details.
Frank
-- 
Frank Heckenbach, frank@g-n-u.de, http://fjf.gnu.de/, 7977168E
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