Page 513: Prior to table, beg and end are described as being predicates instead of iterators.

[WraithGlade]

Here's the text in question:

In this table, r is a string range, and beg and end are element comparison predicates.

I haven't used this Boost function yet, but it looks very likely that you accidentally wrote the wrong thing here.

[JLospinoso]

Thanks, @WraithGlade!