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Re: get_i [message #54350 is a reply to message #54247]

Thu, 02 July 2020 22:08

Novo
Messages: 1430
Registered: December 2006

Ultimate Contributor

Sorry for the late response.
My code is correct. Temporary String lives only during function call. This is how C++ works.
Return type is a value, not a reference. So, no temporaries ...

"The type of the ternary ?: expression is the common type of its second and third argument. If both types are the same, you get a reference back. If they are convertable to each other, one gets chosen and the other gets converted (promoted in this case). Since you can't return an lvalue reference to a temporary (the converted / promoted variable), its type is a value type."

Basically, the ternary ?: is needed to convert "const char[N]" and "const char[M]" to "const char*".

On the other side, templates is a complicated thing.
If you have a non-template version of "decode" declared before template instantiation point, compiler will choose it ...
Also MSVC is very well known for broken "two-phase name lookup". Even till these days, I believe ...
IMHO, a safer version would look like this:

namespace details {
	template <class T, class V>
	constexpr auto decode(const T& sel, const V& def)
	{
		return def;
	}
	
	template <class T, class K, class V, typename... L>
	constexpr auto decode(const T& sel, const K& k, const V& v, const L& ...args)
	{
		return sel == k ? v : details::decode(sel, args...);
	}
}
	
template <class T, class K, class V, typename... L>
constexpr auto decode(const T& sel, const K& k, const V& v, const L& ...args)
{
	return details::decode(sel, k, v, args...);
}

Regards,
Novo

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