e> is a constant integral expression specifying the index of the element to be accessed.
Depending on whether <code>t</code> is const or not, <code>get</code> returns the <code>N</code>th element as a reference to const or
non-const type.
The index of the first element is 0 and thus<code>
N</code> must be between 0 and <code>k-1</code>, where <code>k</code> is the number of elements in the tuple. 
Violations of  these constrains are detected at compile time. Examples:

<pre><code>double d = 2.7; A a;
tuple&