X4Movable (all overloads of x4::move_to(src, dst)) should be SFINAE-friendly

Some classes use X4Movable to show human-friendly errors but in return the current implementation of X4Movable is not SFINAE-friendly in certain scenario.

Generically speaking, any concept should be SFINAE-friendly. We should fix X4Movable while keeping human-friendly errors in all usages.

The overload below should ideally be = delete("with reason"); but it's not implemented in C++23. How can we solve this issue?

x4/include/iris/x4/core/move_to.hpp

Lines 68 to 84 in e811b03

    
           template<traits::NonUnusedAttr T> 
        
           constexpr void move_to(T&, T&) noexcept 
        
           { 
        
               static_assert( 
        
                   !std::is_const_v<T>, 
        
                   "`x4::move_to(T const&, T const&)` is not allowed" 
        
               ); 
        
               static_assert( 
        
                   false, 
        
                   "lvalue reference detected on the `src` argument of `x4::move_to`. " 
        
                   "The caller is definitely lacking `std::move` or `std::forward`. If you " 
        
                   "intend to *copy* the mutable value, apply `x4::move_to(std::as_const(attr_), attr)`." 
        
               ); 
        
               // Banned: possible, but bug-prone. 
        
               // dest = std::move(src); 
        
           }

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`X4Movable` (all overloads of `x4::move_to(src, dst)`) should be SFINAE-friendly #45

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	template<traits::NonUnusedAttr T>
	constexpr void move_to(T&, T&) noexcept
	{
	static_assert(
	!std::is_const_v<T>,
	"`x4::move_to(T const&, T const&)` is not allowed"
	);

	static_assert(
	false,
	"lvalue reference detected on the `src` argument of `x4::move_to`. "
	"The caller is definitely lacking `std::move` or `std::forward`. If you "
	"intend to copy the mutable value, apply `x4::move_to(std::as_const(attr_), attr)`."
	);
	// Banned: possible, but bug-prone.
	// dest = std::move(src);
	}

X4Movable (all overloads of x4::move_to(src, dst)) should be SFINAE-friendly #45

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`X4Movable` (all overloads of `x4::move_to(src, dst)`) should be SFINAE-friendly #45