gsl::span works differently than std::span in terms of type matching? about gsl-lite

[mbeutel]

What do I miss?

Modern defaults. The code compiles fine with version-1 defaults (godbolt).

The ambiguity stems from an unconstrained conversion constructor which has been deprecated a while ago. It is replaced by a constrained version if modern defaults are enabled:

gsl-lite/include/gsl/gsl-lite.hpp

Lines 3770 to 3784 in 34ba514

	#if ! gsl_DEPRECATE_TO_LEVEL( 5 )
	template< class U, size_t N >
	gsl_api gsl_constexpr span( U (&arr)[N] ) gsl_noexcept
	: first_( gsl_ADDRESSOF( arr[0] ) )
	, last_ ( gsl_ADDRESSOF( arr[0] ) + N )
	{}
	#else
	template< size_t N
	gsl_ENABLE_IF_(( std::is_convertible<value_type(*)[], element_type(*)[] >::value ))
	>
	gsl_api gsl_constexpr span( element_type (&arr)[N] ) gsl_noexcept
	: first_( gsl_ADDRESSOF( arr[0] ) )
	, last_ ( gsl_ADDRESSOF( arr[0] ) + N )
	{}
	#endif // deprecate

To enable version-1 defaults, define the preprocessor macro gsl_CONFIG_DEFAULTS_VERSION=1, or if you consume gsl-lite via CMake, simply reference the gsl::gsl-lite-v1 target rather than just gsl::gsl-lite. See https://github.com/gsl-lite/gsl-lite#version-semantics for more details on semantic differences between the versioned defaults.

[harsszegi]

Yeeha, and of course it works just fine! Thanks a lot @mbeutel !