Why this works (Templates, SFINAE). C++

c++, sfinae, templates

Solution

I assume you are refering to the Yes enum? `IsClassT<T>::test<T>(0)`? sizeof does not actually evaluate its arguments. That's why code like the following is legal, even though you might expect it to bail out on you:

int* p = 0;
int sizeof_int = sizeof(*p); //oops, p is 0 :(

Problem

referring to yesterday's post, this woke me up this morning. Why does this actually work? As long as the function `test` is concerned, this function has no body so how can it perform anything? I want to know why and how this works? I'm REALLY interested to see your answers. ``` template<typename T> class IsClassT { private: typedef char One; typedef struct { char a[2]; } Two; template<typename C> static One test(int C::*); //NO BODY HERE template<typename C> static Two test(…); //NOR HERE public: enum { Yes = sizeof(IsClassT<T>::template test<T>(0)) == sizeof(One) }; enum { No = !Yes }; }; ``` Thanks in advance with help to understand this very interesting phenomenon.

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