Compilation error while adding two shorts

[Ali Çehreli via Digitalmars-d-learn]

On 06/23/2014 10:03 PM, David Zaragoza wrote:> Hello
 >
 > I'm trying to compile the following program:
 >
 > module main;
 >
 > int main(string[] argv){
 >      short asd = 1;
 >      short qwe = asd + asd;
 >      return 0;
 > }
 >
 > And the compiler gives this error:
 >
 > C:\David>dmd simple
 > simple.d(5): Error: cannot implicitly convert expression (cast(int)asd +
 > cast(in
 > t)asd) of type int to short
 >
 > Why is there a cast if I'm adding to shorts?
 >
 > Regards

This is a common gotcha of system languages like C, C++, and D. 
Operations like + are never executed in types like 'short'.[1] Since the 
result of that + is int, the compiler does not allow assigning the value 
back to a short, which can lose data.

However, in this case it is clear that the value of asd is known to be 1 
at compile time and that there will not be data loss. The D compilers 
apply what is known as 'value range propagation'[2], which should take 
care of your issue. I guess the use in your program is too complicated 
for the current compiler.

Ali

[1] See both "Integer Promotions" and "Usual Arithmetic Conversions" here:

   http://dlang.org/type.html

[2] "Value Range Propagation"

   http://www.drdobbs.com/tools/value-range-propagation/229300211