How can I get a Docker image’s label if the label name has a “.” in it?
The index function is what I was looking for. It can lookup arbitrary strings in the map. $ docker inspect -f ‘{{ index .Config.Labels “com.wherever.foo” }}’ foo bang
templates
Why can’t templates be declared in a function?
The problem is probably linked to the historical way templates were implemented: early implementation techniques (and some still used today) require all symbols in a template to have external linkage. (Instantiation is done by generating the equivalent code in a separate file.) And names defined inside a function never have linkage, and cannot be referred … Read more
How do I implement no-op macro (or template) in C++?
While leaving it blank is the obvious option, I’d go with #define conditional_noop(x) do {} while(0) This trick is obviously no-op, but forces you to write a semicolon after conditional_noop(123).
How do I get the return type of a member function without an object?
You don’t need that- remember that since decltype doesn’t evaluate its argument, you can just call on nullptr. decltype(((T*)nullptr)->foo()) footype;
Is it possible to have a constructor template with no parameters?
There is no way to explicitly specify the template arguments when calling a constructor template, so they have to be deduced through argument deduction. This is because if you say: Foo<int> f = Foo<int>(); The <int> is the template argument list for the type Foo, not for its constructor. There’s nowhere for the constructor template’s … Read more
template argument deduction/substitution failed, when using std::function and std::bind
To figure out the problem let separate statements: auto f = bind(&TestA::testa, &testA, _1, _2); // OK test.setCallback(f); // <<— Error is here setCallback needs to know type of T and it can’t deduce it from f, so give it a type test.setCallback<TYPE>(f); // TYPE: int, float, a class, …
GCC(/Clang): Merging functions with identical instructions (COMDAT folding)
Neither GCC nor Clang is a linker, and ICF needs to be done by the linker, or at least with cooperation with the linker. Edit: They don’t do ICF, so yes, distinct instantiations produce distinct code. The GNU gold linker supports ICF with the –icf option, which needs the GCC option -ffunction-sections to be used. … Read more
What’s the right way to specialize a template when using “extern template”?
extern template class A<long>; This line says that A<long> is to be explicitly instantiated according to the definitions the compiler has already seen. When you add a specialization later, you break that meaning. Add a declaration of your specialization to the header file. template <typename T> struct A { /*…*/ }; template<> int A<long>::get() const; … Read more
Creating an interface for an abstract class template in C++
You are actually attempting the impossible. The very heart of the matter is simple: virtual and template do not mix well. template is about compile-time code generation. You can think of it as some kind of type-aware macros + a few sprinkled tricks for meta programming. virtual is about runtime decision, and this require some … Read more
std::vector as a template function argument
The right way for a template function to accept any std::vector by const& is: template<typename T, typename A> void some_func( std::vector<T,A> const& vec ) { } the second argument is the “allocator”, and in some advanced usage of std::vector it will not be the default one. If you just accept std::vector<T>, your some_func will reject … Read more