The forward-declaration method is almost always better. (I can’t think of a situation where including a file where you can use a forward declaration is better, but I’m not gonna say it’s always better just in case). There are no downsides to forward-declaring classes, but I can think of some downsides for including headers unnecessarily: … Read more
Great question. I use a pattern like this for most of my scripts: #!/bin/bash main() { foo bar baz } foo() { } bar() { } baz() { } main “$@” You can read the code from top to bottom, but it doesn’t actually start executing until the last line. By passing “$@” to main() … Read more
This is how you would do it: template<typename Type, typename IDType=typename Type::IDType> class Mappings; template<typename Type, typename IDType> class Mappings { public: … Type valueFor(const IDType& id) { // return value } … }; Note that the default is in the forward declaration and not in the actual definition.
This is simply not possible. You cannot forward declare a nested structure outside the container. You can only forward declare it within the container. You’ll need to do one of the following Make the class non-nested Change your declaration order so that the nested class is fully defined first Create a common base class that … Read more
That basically means that you need to import the .h file containing the declaration of States. However, there is a lot of other stuff wrong with your code. You’re -init’ing an object without +alloc‘ing it. That won’t work You’re declaring an object as a non-pointer type, that won’t work either You’re not calling [super init] … Read more
You can’t do it, it’s a hole in the C++ language. You’ll have to un-nest at least one of the nested classes.
Wrap the invocation into a function of its own so that foo() def foo(): print “Hi!” will break, but def bar(): foo() def foo(): print “Hi!” bar() will work properly. The general rule in Python is that a function should be defined before its usage, which does not necessarily mean it needs to be higher … Read more
You can do forward typedef. But to do typedef A B; you must first forward declare A: class A; typedef A B;
Why forward-declare is necessary in C++ The compiler wants to ensure you haven’t made spelling mistakes or passed the wrong number of arguments to the function. So, it insists that it first sees a declaration of ‘add’ (or any other types, classes, or functions) before it is used. This really just allows the compiler to … Read more
Put yourself in the compiler’s position: when you forward declare a type, all the compiler knows is that this type exists; it knows nothing about its size, members, or methods. This is why it’s called an incomplete type. Therefore, you cannot use the type to declare a member, or a base class, since the compiler … Read more