please approval my patch - add new logical traits to type_traits for logical completeness

[Jonathan Wakely]

On 10/02/19 11:46 +0800, 李苏旺 wrote:
>hi Marc,
>    I am very glad to receive you reply, in fact , I have neither "  C++
>standard these are specified" nor "feature test macro" , I saw negation,
>conjunction and disjunction have added in type_traits , and similar , after
>I reference to
>https://whatis.techtarget.com/definition/logic-gate-AND-OR-XOR-NOT-NAND-NOR-and-XNOR#xnor
>  , I think  XOR(exclusive_or), NAND(not_conjunction),
>NOR(not_disjunction), XNOR(not_exclusive_or) can be added in type_traits ,
>that is all . any way , thank you reminder , maybe I may write a proposal
>in the future , I hope these logical gates can be added too

I agree with Marc that we don't want to add these, unless they are
first added to the C++ standard (and I don't think they are useful
enough to add to the standard either).