Saturday, 16 September 2017

c++11 - C++ 'typedef' vs. 'using ... = ...'






Possible Duplicate:
What are the differences between typedef and using in C++11?






The following code compiles and runs. My question is what is the difference between the "typedef" and "using" method for renaming the template specialization?




template
struct myTempl{
T val;
};

int main (int, char const *[])
{
using templ_i = myTempl;
templ_i i;

i.val=4;

typedef myTempl templ_f;
templ_f f;
f.val=5.3;

return 0;
}



Edit:



If there is no difference, which one would you prefer? / Why was the using ... = ... version introduced?


Answer



They are the same.



To quote the C++11 standard (or the draft to be specific):




A typedef-name can also be introduced by an alias-declaration. The identifier following the using keyword

becomes a typedef-name and the optional attribute-specifier-seq following the identifier appertains to that
typedef-name. It has the same semantics as if it were introduced by the typedef specifier. In particular, it
does not define a new type and it shall not appear in the type-id.




I think the "the same semantics as the typedef specifier" say it all.


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