Some Boost.Range adaptors, such as 'transformed' or 'filtered', require a unary function. The documentation does not formally define "unary function", but it's pretty clear what it ought to be: a function (object) that's callable with one argument.
Thus, to me, the following is a perfectly valid unary function:
int foo(int a, int b = 0);
as it is callable with one argument.
However, Boost.Range does not accept such a function as an argument to 'transformed' or 'filtered'.
[snip]
Would it be possible to treat N-ary functions with N-1 default arguments as unary?
To motivate this request a bit further, suppose 'foo' is a function in some library, so that I can't just replace it with two overloads, and consider possible workarounds: 1. range | transformed(bind(foo, _1, let_me_repeat_the_default_arg_here)); 2. range | transformed([](let_me_write_out_the_type_of_foo's_argument_here x) { return foo(x); }) The first requires repeating the library function's default argument, which introduces a risk of the actual behaviour becoming out of sync with the desired behaviour if the default argument used by the library changes. (Note that simply bind(foo, _1) will not work - it produces similar errors). The second is messy (and would be even more so in C++03) and requires writing out the potentially long type name of the function's argument. I can't think of anything better at the moment. Regards, Nate