C++ Primer Plus

for (auto p = il.begin(); p !=il.end(); p++)

decltype

The decltype keyword creates a variable of the type indicated by an expression. The following statement means “make y the same type as x,” where x is an expression:

decltype(x) y;

Here are a couple of examples:

double x;

int n;

decltype(x*n) q; // q same type as x*n, i.e., double

decltype(&x) pd; // pd same as &x, i.e., double *

This is particularly useful in template definitions, when the type may not be determined until a specific instantiation is made: