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In C++11 you can create a "type alias" by doing something like
template <typename T>
using stringpair = std::pair<std::string, T>;
But this is a deviation from what you'd expect a template typedef would look like:
template <typename T>
typedef std::pair<std::string, T> stringpair;
So this raises the question - why did they need to come up with a new syntax? what was it that did not work with the old typedef syntax?
I realize the last bit doesn't compile but why can't it be made to compile?
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A typedef is scoped exactly as the object declaration would have been, so it can be file scoped or local to a block or (in C++) to a namespace or class.
The typedef keyword allows the programmer to create new names for types such as int or, more commonly in C++, templated types--it literally stands for "type definition". Typedefs can be used both to provide more clarity to your code and to make it easier to make changes to the underlying data types that you use.
Syntax. Note that a typedef declaration does not create types. It creates synonyms for existing types, or names for types that could be specified in other ways.
The typedef declaration provides a way to declare an identifier as a type alias, to be used to replace a possibly complex type name.
I'll just refer to stroustrup himself:
http://www.stroustrup.com/C++11FAQ.html#template-alias
The keyword using is used to get a linear notation "name followed by what it refers to." We tried with the conventional and convoluted typedef solution, but never managed to get a complete and coherent solution until we settled on a less obscure syntax.
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