Why can't the template argument be deduced when it is used as template parameter to another template?

Question

What is wrong in this code?

#include 

Answer 1

Even you have:

TMap::Type = std::map. 

But before you call test(tmap)

TMap::Type tmap;
tmap[1.1] = 5.2;
double d = test(tmap); 

You already have it declared as

TMap::Type tmap;

why this information can not be utilized. #typedef is not just simple string replacement.