The behavior is undefined. [meta.unary.prop] template <class T, class… Args> struct is_constructible; T and all types in the parameter pack Args shall be complete types, (possibly cv-qualified) void, or arrays of unknown bound. That’s a precondition of the meta-function. A contract that your code violates. libc++ is being generous by notifying you. Mind you, that … Read more
The clause “If a conversion function is a member function,” was added to the working draft in N2798 as part of the Concepts wording per N2773 Proposed Wording for Concepts. N2798 12.3.2/1 reads (I’ll use bold to show additions, and strikeout to show removals): 1 A member function of a class X having no parameters, … Read more
Both assertions succeed because they are applied to the type T deduced from function argument. In both cases it will be deduced as a pointer to function because functions decay to a pointer to function. However if you rewrite assertions to accept types directly then first one will fail: static_assert(is_same<void(*)(), decltype(fun)>::value); static_assert(is_same<void(*)(), decltype(&fun)>::value); online compiler
Possible in theory (along with unused public members), but not with the kind of compiler ecosystem we’re used to (targeting a fixed ABI that can link separately-compiled code). Removing unused members could only be done with whole-program optimization that forbids separate libraries1. Other compilation units might need to agree on sizeof(foo), but that wouldn’t be … Read more
tl;dr: The sequence of the modifications and reads performed in (i+=10)+=10 is well defined in both C++98 and C++11, however in C++98 this is not sufficient to make the behavior defined. In C++98 multiple modifications to the same object without an intervening sequence-point results in undefined behavior, even when the order of those modifications is … Read more
Why isn’t void a primitive type? Because it isn’t something you can instantiate. It isn’t a primitive type, nor a reference type. It is nothing at all. Eric Lippert describes some ‘problems’ with the void type in this post on Software Engineering, which goes into the specifics of void as a type to use in … Read more
UPDATE: This question was the subject of my blog on June 18th, 2012. Thanks for the great question! Why? I want to know if this was a design decision and if so, what prompted it? You are essentially asking for the minutes of the meeting of the ANSI C design committee, and I don’t have … Read more
Is it even possible for the result of i-j not to be in the range of representable values of ptrdiff_t? Yes, but it’s unlikely. In fact, [support.types.layout]/2 does not say much except the proper rules about pointers subtraction and ptrdiff_t are defined in [expr.add]. So let us see this section. [expr.add]/5 When two pointers to … Read more
I’m surprised no one has mentioned this cheap counterexample yet: struct foo { static foo f; // might seem dubious but doesn’t violate anything void* operator new(size_t, void* p) {return &f;} }; Demo on Coliru. Unless a class-specific placement version is called, however, your assertion should hold. Both expressions have to represent the same address … Read more
The size limit of an object is implementation defined, per Annex B of the standard [1]. Your struct is of an absurd size. If the struct is: struct Foo { char arr1[INT_MAX]; //char arr2[INT_MAX]; char ch1; char ch2; }; … the size of your struct in a relatively recent version of 64-bit MSVC appears to … Read more