Enlightening Usage of C++11 decltype

Question

I\'ve just seen this really nice talk Rock Hard: C++ Evolving by Boris Jabes. In the section of the talk concerning Higher-Order Generic Programming he say

Answer 1

One place that I use it, is where I need to make a variable that must have same type of another variable . but I'm not sure if in future the type will stay same or not .

void foo(int a)//maybe in future type of a changed
{
    decltype(a) b;
    //do something with b
}