This is [dcl.spec.auto/11]: If the type of an entity with an undeduced placeholder type is needed to determine the type of an expression, the program is ill-formed. Once a non-discarded return statement has been seen in a function, however, the return type deduced from that statement can be used in the rest of the function, … Read more
The whole point of make_unique is to encapsulate the notion of “use new to create a T from given constructor arguments and use delete to destroy it”. If you wanted a custom deleter, you would also have to specify how to create the object, and then there would be nothing more gained from having the … Read more
Disclaimer: I’m the author of the char8_t P0482 and P1423 proposals. In C++20, char8_t is a distinct type from all other types. In the related proposal for C, N2653, char8_t is a typedef of unsigned char similar to the existing typedefs for char16_t and char32_t. In C++20, char8_t has an underlying representation that matches unsigned … Read more
I think the place you are stumbling is actually with the expression c.getObj() in the line return c.getObj();. You think the expression c.getObj() has type const Int&. However that is not true; expressions never have reference type. As noted by Kerrek SB in comments, we sometimes talk about expressions as if they had reference type, … Read more
but I can’t see anything in the standard that therefore allows me to reinterpret_cast between them, even though that seems like the reasonable interpretation of “value representation”. Is this technically allowed by the standard? No. The standard is clear (see [basic.lval] p10) about which types can be aliased, and layout-compatible types are not included. If … Read more
The problem originates from the following post-condition of std::vector<T>::resize, [vector.capacity]: Remarks: If an exception is thrown other than by the move constructor of a non-CopyInsertable T there are no effects. That is, a vector must remain unchanged if relocation fails. One of the reasons relocation may fail is due to an exception, specifically, when a … Read more
The One Definition rule tells us that we can not have more than one definition of an odr-used variable in a program. So if a variable is odr-used then you need to define it but you can not define it the header file since it may be included more than once with the whole program. … Read more
This is now supported properly from Qt 5.4. You just type this into your qmake project file: CONFIG += c++14 The necessary code change went in the middle of 2014 by Thiago: Add support for CONFIG += c++14 I have just created the necessary documentation change: Mention the c++14 CONFIG option in the qmake variable … Read more
I believe clang is correct here. We can see from the draft C++ standard section 6.4.2 The switch statement that this involves a contextually implicit conversion. Paragraph 2 says (*emphasis mine going forward): The condition shall be of integral type, enumeration type, or class type. If of class type, the condition is contextually implicitly converted … Read more
In C++14, std::set<Key>::find is a template function if Compare::is_transparent exists. The type you pass in does not need to be Key, just equivalent under your comparator. So write a comparator: template<class T> struct pointer_comp { typedef std::true_type is_transparent; // helper does some magic in order to reduce the number of // pairs of types we … Read more