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Sc4Freak

[C++] Choosing a class specialization based on type size

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Hi, I have a templated class which operates as a data store and handler. It has two internal implementations - one optimised for smaller data types (less than around 8 bytes) and one optimised for larger data types. But how do I do a compile-time class specialization based on type size, and not the type itself? I know sizeof() doesn't work in the preprocessor, so I can't use the preprocessor to separate out the implementations based on the type size. Is there any other way to do this?

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You can use non-type template parameters like bool:

template <bool big>
class A {
// big data
};

template <>
class A<false> {
// little data
};

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More fancily you can do this:
template <typename T>
class B {
private:
//insert SiCrane's code here
B::A<(sizeof(T)>8)> data;
public:
//method example
int getData() {return data->getData();}
};




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You can specialize based on size like this:


template<typename T, int size=sizeof(T)>
struct Foo;

template<typename T>
struct Foo<T, 1>
{
...
};


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