Thanks for your replies.
I have performed some profiling with Clang passing a `path` to the lambda instead of `const char*` and the performance gain are effectively reduced as stated by Nicol Bolas.
For this reason, i have changed the proposal to add both solutions: a new recursive_directory_iterator constructor with predicate concept on `path` ( for generality) and a new recursive_directory_iterator constructor with predicate concept on `const char *` (mostly for performance gain, as profiling shows, we can divide execution time by two, and even more..)
I have added a subsection "Passing a path or passing const char* to the predicate concept" at "Analysis and Discussions" section, explaining this, and have taken into account your other comments.
Please, find attached the new draft proposal.