* make FCS get and conversion-operator methods const
etl::frame_check_sequence has to access methods which can be made const:
value_type value() const
operator value_type() const
* make jenkins_policy::initial and final const
According to the documentation, initial, add and const have to be
tagged as const.
final has to be const now due to the change in the previous commit which
makes the fcs getter methods const.
* add missing overloads for span::first + span::last
The C++20 standard defines additional overloads for first and last:
template< std::size_t Count >
constexpr std::span<element_type, Count> first() const;
constexpr std::span<element_type, std::dynamic_extent> first( size_type Count ) const;
template< std::size_t Count >
constexpr std::span<element_type, Count> last() const;
constexpr std::span<element_type, std::dynamic_extent> last( size_type Count ) const;
etl implements only the first (= template) variants so far. To be able to
compile valid C++20 code the missing overload should be added.
* remove explicit specifier for span conversion operator
The C++20 standard allows to assign a span of non-const elements to a span of
const elements. Example:
std::span<const int> cintspan;
std::span<int> intspan;
cintspan = intspan;
This is enabled in the STL by using an explicit specifier with a constant
expression for one of the conversion constructors:
template< class R >
explicit(extent != std::dynamic_extent)
constexpr span( R&& r );
The explicit specifier together with a constant expression is a C++20 feature
and therefore can't be used within etl. To be able to compile valid C++20
code which uses the conversion on assignment, the explicit specifier has to
be removed.
* remove explicit specifier for span conversion operator
The C++20 standard allows to assign an array of elements directly (without
explicitly using a conversion constructor). Example:
const int data = { 1, 2, 3 };
std::span<const int> cintspan;
cintspan = data;
To be able to compile valid C++20 code which uses the conversion on assignment,
the explicit specifier of the array-conversion constructor has to be removed.
