The transparent operator functors proposal is there as a way to have generalised functors that are located in <functional>. I personally believe the proposal itself has a very good example that would help illustrate the need for it. However I’ll go ahead and try to explain it as well. Suppose you have a function, a … Read more
Unfortunately, even x86-64 implementations can differ – from Intel’s instruction set reference,BSF and BSR, with a source operand value of (0), leaves the destination undefined, and sets the ZF (zero flag). So the behaviour may not be consistent between micro-architectures or, say, AMD and Intel. (I believe AMD leaves the destination unmodified.) The newer LZCNT … Read more
What are the rules here? As there is only one parameter, the rule is that one of the three viable parameter initializations of that parameter must be a better match than both the other two. When two initializations are compared, either one is better than the other, or neither is better (they are indistinguishable). Without … Read more
Is there a way to cause a compile-time error with a constexpr function, but not do anything at run time? You can use the exact same trick, but instead of using a throw-expression, use an expression that is not a constant expression but does what you want at runtime. For instance: int runtime_fallback(int x) { … Read more
No, it can not. That functionality was proposed to the committee under the name upgrade_mutex and upgrade_lock, but the committee chose to reject that portion of the proposal. There is currently no work under way to re-prepose that functionality. Edit In response to the “where to go from here” edit in user3761401’s question, I’ve created … Read more
The rules have always been as follows: A const static data member (SDM) of integral or enumeration type can be initialised in class with a constant expression. A constexpr SDM must be initialised in class with a constant expression. C++17 no longer requires an initializer when the default constructor initialises every member. Also, constexpr SDMs … Read more
Caveat: I stand by this answer since I think it presents a best practice which will improve ~95% of C++ code – probably even more. That said, please read the full comments for a discussion of some important caveats. Since it was my comment, here’s my presentation explaining this. In a nutshell: [Raw] pointers must. not. … Read more
The following MyTest testObj = {}; is not zero-initialization for MyTest, but is simply calling its default constructor. The cppreference page explains why (emphasis mine): As part of value-initialization sequence for non-class types and for members of value-initialized class types that have no constructors, including value initialization of elements of aggregates for which no initializers … Read more
This syntax is slightly different. First, because types are easier to work with than packs, a type that holds a pack. The using type=types; just saves me work in the code that generates a types: template<class…>struct types{using type=types;}; Here is the workhorse. It takes a signature, and produces a types<?…> bundle containing the arguments for … Read more
Disclaimer: ‘stack’ is not part of the c++ standard to my knowledge, there we have ASDVs (automatic storage duration variables). ABI might define stack. Note that sometimes these are passed in registers, which I believe is OK in your case. Define a CPS (continuation-passing style) factory method: class A { public: template<typename F, typename… Args> … Read more