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Span: Allow copy construction from convertible span. 

Addition of these overloads help when Span<const T> is constructed from Span<T>.
pull/7828/head
Vincent Coubard 2018-08-23 18:41:53 +01:00
parent b7f074ef68
commit d5051a8ca7
1 changed files with 57 additions and 3 deletions
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60
platform/Span.h
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@ -25,6 +25,36 @@
namespace mbed {
// Internal details of span
// It is used construct span from span of convertible types (non const -> const)
namespace span_detail {
// If From type is convertible to To type then the compilation constant value is
// true otherwise it is false.
template<typename From, typename To>
class is_convertible
{
struct true_type { char x[512]; };
struct false_type { };
static const From& generator();
static true_type sink(const To &);
static false_type sink(...);
public:
static const bool value = sizeof(true_type) == sizeof(sink(generator()));
};
template<bool Condition, typename ResultType = void>
struct enable_if;
template<typename ResultType>
struct enable_if<true, ResultType> {
typedef ResultType type;
};
}
/**
* Special value for the Extent parameter of Span.
* If the type use this value then the size of the array is stored in the object
@ -269,6 +299,24 @@ struct Span {
Span(element_type (&elements)[Extent]):
_data(elements) { }
/**
* Construct a Span object from another Span of the same size.
*
* @param other The Span object used to construct this.
*
* @note For span with a positive extent, this function is not accessible.
*
* @note OtherElementType(*)[] should be convertible to ElementType(*)[].
*/
template<typename OtherElementType>
Span(
const Span<OtherElementType, Extent> &other,
typename span_detail::enable_if<
span_detail::is_convertible<OtherElementType (*)[], ElementType (*)[]>::value
>::type* = 0
):
_data(other.data()) { }
/**
* Return the size of the sequence viewed.
*
@ -540,16 +588,22 @@ struct Span<ElementType, SPAN_DYNAMIC_EXTENT> {
Span(element_type (&elements)[Count]):
_data(elements), _size(Count) { }
/**
* Construct a Span object from another Span.
*
* @param other The Span object used to construct this.
*
* @note For span with a positive extent, this function is not accessible.
*
* @note OtherElementType(*)[] should be convertible to ElementType(*)[].
*/
template<ptrdiff_t OtherExtent>
Span(const Span<element_type, OtherExtent> &other):
template<typename OtherElementType, ptrdiff_t OtherExtent>
Span(
const Span<OtherElementType, OtherExtent> &other,
typename span_detail::enable_if<
span_detail::is_convertible<OtherElementType (*)[], ElementType (*)[]>::value
>::type* = NULL
):
_data(other.data()), _size(other.size()) { }
/**