Is it possible to take a parameter by const reference, while banning conversions so that temporaries aren't passed instead?

Question

Sometimes we like to take a large parameter by reference, and also to make the reference const if possible to advertize that it is an input parameter. But by making the refe

Answer 1

If you can use C++11 (or parts thereof), this is easy:

void f(BigObject const& bo){
  // ...
}

void f(BigObject&&) = delete; // or just undefined

Live example on Ideone.

This will work, because binding to an rvalue ref is preferred over binding to a reference-to-const for a temporary object.

You can also exploit the fact that only a single user-defined conversion is allowed in an implicit conversion sequence:

struct BigObjWrapper{
  BigObjWrapper(BigObject const& o)
    : object(o) {}

  BigObject const& object;
};

void f(BigObjWrapper wrap){
  BigObject const& bo = wrap.object;
  // ...
}

Live example on Ideone.