* Add usage for check-and-unwrap of MS STL iterators
This is Billy ONeal's PR #682 with a typo fixed.
See corresponding change here:
ca77129308
That change officially exposes the STL's range checking machinery,
available in MSVC++ "15.8"+
This change augments GSL span::iterator to call into that newly exposed
machinery.
_Verify_range(cit, cit)
Requests that the iterator type check that the parameters form a valid
[First, Last) range iterator pair. This replaces _DEBUG_RANGE and
supporting machinery. The standard library provides a version for
pointers under _IDL != 0; otherwise they are normally provided via
hidden friend functions. Note that declaring some of these hidden
friends for "wrapper" iterators like move_iterator and reverse_iterator
triggers VSO#610735.
cit._Verify_offset(difference_type _Off)
For random-access iterators, performs any asserts that would be
performed by i += _Off; except with possibly a better error message and
without moving the iterator.
cit._Unwrapped()
Returns an "unchecked" or "unwrapped" iterator which has previously been
validated. The iterator may have been validated by a call to
_Verify_range or _Verify_offset (above), or by seeking a checked
iterator to a "high water mark" point.
it._Seek_to(cit) / it._Seek_to(return value from _Unwrapped())
Moves the position of the checked iterator it to the position of the
unchecked iterator supplied. Generally not intended to perform range
checks.
* Fixed build break in VS2015
* fixed constexpr build break when using VS2015
51ae678d08