cpp/ranges/slide view/iterator/iterator

Construct an iterator.

@1@ Default constructor. Value-initializes the underlying data members:
 * with ,
 * with (note that this member may not be present),
 * with.

@2@ Conversion from to. Initializes the underlying data members: Note that can only be formed when  models, in which case  is not present.
 * with ,
 * with.

@3@ A private constructor which is used by ranges and ranges. This constructor is not accessible to users. Initializes the underlying data members: Note that this overload can only be present if is not present.
 * with ,
 * with.

@4@ A private constructor which is used by ranges and ranges. This constructor is not accessible to users. Initializes the underlying data members:
 * with ,
 * with (note that this data member is present due to  requirement),
 * with.