Please see edits below! For Each edits also added below under Edit2 More edits about ForEach and Collections at Edit3 One last edit about ForEach and Collections at Edit4 A final note about iteration behavior at Edit5 Part of the subtlety of this odd behavior in the semantics of variant evaluation when used as a … Read more
There’s an open clang report that cover the case of implicit capture of references by lambda expressions, this is not limited to std::cout but to references variable that are found to refer to constant expressions. For more reference, the backing defect report on the CWG is CWG-1472 EDIT: Based on @Rakete1111 comment, I should have … Read more
This is definitely a compiler bug, and actually one that has been known for quite some time: GCC #47346 (first reported in Jan 2011) and Clang #15914 (first reported May 2013). Your __tklass is clearly private, and the template alias is not marked friend, so this should be a simple access error. The simplest reproduction … Read more
There are apparently existing implementations that optimize based on this. Consider: struct A { double x[4]; int n; }; void g(double* p); int f() { A a { {}, 42 }; g(&a.x[1]); return a.n; // optimized to return 42; // valid only if you can’t validly obtain &a.n from &a.x[1] } Given p = &a.x[1];, … Read more
I do not see any particular reason why deduction guide couldn’t have a explicit-specifier. Me neither. Seems like a total oversight on my part (I’m one of the authors of conditional explicit). I’ll try to file a core issue. Update: This was fixed in P1968, adopted in Belfast, as part of the resolution for core … Read more
The requirements of the call to the function object Deleter are specific on this as listed in the requirements of the std::unique_ptr<T>::reset() member. From [unique.ptr.single.modifiers]/3, circa N4660 §23.11.1.2.5/3; unique_ptr modifiers void reset(pointer p = pointer()) noexcept; Requires: The expression get_deleter()(get()) shall be well formed, shall have well-defined behavior, and shall not throw exceptions. In general … Read more
Does the definition int a = 0, b = a++, c = a++; have defined behavior in C? Yes, because C 2018 6.8 3 says these initializations (not all, see bottom) are evaluated in the order they appear: … The initializers of objects that have automatic storage duration, and the variable length array declarators of … Read more
This is an odd aspect of C++’s lifetime rules. [basic.life]/1 tells us that an object’s lifetime ends: if T is a class type with a non-trivial destructor ([class.dtor]), the destructor call starts, or the storage which the object occupies is released, or is reused by an object that is not nested within o ([intro.object]). Emphasis … Read more
Explicit and unequivocal NO. Standard doesn’t have this guarantee, and this is why try_emplace exists. See notes: Unlike insert or emplace, these functions do not move from rvalue arguments if the insertion does not happen, which makes it easy to manipulate maps whose values are move-only types, such as std::map<std::string, std::unique_ptr<foo>>. In addition, try_emplace treats … Read more
The wording has changed in various editions of the C++ standard, and in the recent draft cited in the question. (See my comments on the question for the gory details.) C++11 says: Other pointer comparisons are unspecified. C++17 says: Otherwise, neither pointer compares greater than the other. The latest draft, cited in the question, says: … Read more