How to static_cast to the type of variable

Question

If I have a variable or member of a known type is there a method that I can static cast to said type without expressly stating the type?

Thus ensuring that should the variable change type in the future a re-compilation will be all that's needed.

A very basic example would be:

int y = 5;
uint32_t x;
x = static_cast< TYPEOF( x ) >( foo );

Now if at some point in the future x needed to change to an int64_t say it would be nice if only the declaration of the variable needed changed and not all the static_cast lines, of which there may be many.

As a personal note, I am compiling with g++ 6 and thus I am able to use c++14 features, though an answer compatible with other versions may benefit others.

Answer 1

只需使用decltype ：

x = static_cast<decltype(x)>(y);

Answer 2

As stated in the comments above the solution is

int y = 5;
uint32_t x;
x = static_cast< decltype( x ) >( y );