Add/Remove data members with template parameters?
-
28-06-2021 - |
题
Consider the following code :
template<bool AddMembers> class MyClass
{
public:
void myFunction();
template<class = typename std::enable_if<AddMembers>::type> void addedFunction();
protected:
double myVariable;
/* SOMETHING */ addedVariable;
};
In this code, the template parameter AddMembers
allow to add a function to the class when it's true
. To do that, we use an std::enable_if
.
My question is : is the same possible (maybe with a trick) for data members variable ? (in a such way that MyClass<false>
will have 1 data member (myVariable
) and MyClass<true>
will have 2 data members (myVariable
and addedVariable
) ?
解决方案
A conditional base class may be used:
struct BaseWithVariable { int addedVariable; };
struct BaseWithoutVariable { };
template <bool AddMembers> class MyClass
: std::conditional<AddMembers, BaseWithVariable, BaseWithoutVariable>::type
{
// etc.
};
其他提示
First off, your code just won't compile for MyClass<false>
. The enable_if
trait is useful for deduced arguments, not for class template arguments.
Second, here's how you could control members:
template <bool> struct Members { };
template <> struct Members<true> { int x; };
template <bool B> struct Foo : Members<B>
{
double y;
};
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