Brian McNamara wrote:
On Wed, Feb 18, 2004 at 05:04:11PM -0300, Fernando Cacciola wrote:
Referencial Integrity and Side Effects: ========================= ... What I'm trying to say is that I don't like the current design were functoids are prescribed to take only reference to const parameters, for a variety of reasons: ... [ a number of good arguments, elided ]
A number of people have voiced similar complaints, and I am gradually being worn down. I think one of the reasons I resist it is that I don't like how boost::lambda has dealt with the issue. Notably, examples like
// From 5.3.2 of the lambda docs //
http://www.boost.org/libs/lambda/doc/ar01s05.html#sect:bind_expressions bind(&A::set_j, a, _1)(k); // a.j == 0, as a copy of a is modified bind(&A::set_j, _1, 1)(a); // a.j == 1
where reference-versus-copy depends upon the precise "timing" of binding a function argument to a value, ...
There is no "precise timing" issue here, the rule is simple. Every argument passed to bind() is copied, whether it is &A::set_j, a, _1, or 1. An example that may illustrate your point is std::cout << _1 where 'std::cout' is taken by reference, versus _1 << 1 where '1' is copied. But std::cout << _1 is just a convenience spelling for ref(std::cout) << _1, which is reference-consistent. It's too prevalent in motivating examples to not warrant special treatment. :-)