What legitimate reasons exist to overload the unary operator&?

Question

Okay, I\'ve been inspired to do some head punching. Seems like overloading operator& leads to not a small amount of pain.

What legitimate cases exis

Answer 1

Four years later, another answer.

Another use I have seen is when you are piggybacking off of the C++ language, but defining your own semantics. Prime example: Boost.Spirit.

Boost.Spirit, in particular Qi for parsing, overloads operators on parsers to provide an EBNF-like syntax for specifying arbitrary parser objects. In particular, the unary & operator is overloaded to provide the And-Predicate Parser.

And-Predicate Parser (&a)

Description

Syntactic predicates assert a certain conditional syntax to be satisfied before evaluating another production. Similar to semantic predicates, eps, syntactic predicates do not consume any input. The and-predicate, &a, is a positive syntactic predicate that returns a zero length match only if its predicate matches.

Example usage:

Basic look-ahead example: make sure that the last character is a semicolon, but don't consume it, just peek at the next character:

test_phrase_parser("Hello ;", lit("Hello") >> &lit(';'), false);

So in short, the unary & here has no relation to pointers at all; it has domain-specific semantics which apply to Qi parser objects.