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Remove useless runtime checks in span implementation (#1029)

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Both checks for Expects(ExtentType::size() != dynamic_extent); in storage_type are always useless. storage_type<ExtentType> is only ever created with ExtentType == extent_type<Extent>, where Extent has type std::size_t and is the extent of the span.

Looking at extent_type<std::size_t Ext>::size():

- if Ext != dynamic_extent, then size() always returns Ext, and therefore size() != dynamic_extent
- if Ext == dynamic_extent, then size() returns extent_type<dynamic_extent>::size_. size_ can only be set via one of two constructors:
  - constexpr explicit extent_type(size_type size), which already does the check in question
  - constexpr explicit extent_type(extent_type<Other> ext) : size_(ext.size()), which simply relies on the other extent's size() method
So there is no way for ExtentType::size() == dynamic_extent.
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dmitrykobets-msft 2022-04-28 14:58:25 -07:00 committed by GitHub
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commit da01eb28db
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include/gsl/span
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@ -706,14 +706,11 @@ private:
template <class OtherExtentType> template <class OtherExtentType>
constexpr storage_type(KnownNotNull data, OtherExtentType ext) constexpr storage_type(KnownNotNull data, OtherExtentType ext)
: ExtentType(ext), data_(data.p) : ExtentType(ext), data_(data.p)
{ {}
Expects(ExtentType::size() != dynamic_extent);
}
template <class OtherExtentType> template <class OtherExtentType>
constexpr storage_type(pointer data, OtherExtentType ext) : ExtentType(ext), data_(data) constexpr storage_type(pointer data, OtherExtentType ext) : ExtentType(ext), data_(data)
{ {
Expects(ExtentType::size() != dynamic_extent);
Expects(data || ExtentType::size() == 0); Expects(data || ExtentType::size() == 0);
} }