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c++templates
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Reputation: 24675

Strange declaration(templates). C++

How can I understand what is declared here: (this is taken from another post on this forum)

template<typename C> static char (&f(ChT<int Fallback::*, &C::x>*))[1];

Here's how I read:

template of static function f called with (ChT<int Fallback::*, &C::x>*), but then I can't make sense why is there an address-of operator and why is there an array?

I'm still learning how to understand C++ declarations, so please explain this slowly and carefully.

Upvotes: 6

Views: 223

Answers (2)

sth
sth

Reputation: 229563

Using some typedefs:

typedef char (&arrayref_t)[1];

This is a reference to an array of characters. The array has one element.

typedef ChT<int Fallback::*, &C::x> tmpl_t;

This is a template class, instantiated with the type "pointer to an int member of the Fallback class", and a member pointer to x in class C.

static arrayref_t f(tmpl_t*);

The function now takes a pointer to a tmpl_t and returns an arrayref_t.

Upvotes: 7

Alexey Malistov
Alexey Malistov

Reputation: 26975

It's important to see return type. So, return type of this function is reference to char[1]; Imagine that f returns something like reference to the following:

char ret[1];

For example

template<typename C> static char (&f(ChT<int Fallback::*, &C::x>*))[1]
{

   static char xx[1] = {'F'};
   return xx;
}

Upvotes: 3

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