While having pass-by-value may be more convenient and occur more often, the counter-intuitiveness of the semantics will lead to subtle bugs in people's code who misunderstand or forget bind's behavior in this area.
A bold prediction in the face of contradictory evidence.
Can you elaborate? You may have no problems understanding the library, but the first time I tried to bind with a reference, I ran into the same confusion. I am speaking from my own limited experience with the library. I've read the documentation: // Start of docs The arguments that bind takes are copied and held internally by the returned function object. For example, in the following code: int i = 5; bind(f, i, _1); a copy of the value of i is stored into the function object. boost::ref and boost::cref can be used to make the function object store a reference to an object, rather than a copy: int i = 5; bind(f, ref(i), _1); // End of docs I know this makes it explicit that you need a ref or cref to have bind store a reference to an object, but there is no reasoning behind this design decision in the documentation, or that I can find in the implementation and I've not stumbled across it in the mail archives. Best, John