I do understand why this produce compile time-error:
short x = 1;
short y = 2;
short z = x + y; // compile-time error
I've grasped why this runs without any issues:
short x = 1;
short y = 2;
x += y; // all right, because of c# specs section 7.17.2
But I've got no clue why this also works:
short x = (short)1 + (short)2;
I expected to get the same compile-time error as in the first example, but it runs successfully... Why?
Since you're using constant values, the compiler can detect that it's allowable, evaluate it at compile time , and let it execute. The generated IL evaluates to the same as typing short x = 3;
.
Note the following also works (for the same reason):
const short x = 1;
const short y = 2;
short z = x + y;
But this fails:
const short x = 32000;
const short y = 32001;
short z = x + y;
Note that this is covered in the C# Language Spec, 6.1.9 Implicit constant expression conversions:
Your last snippet just compiles to constant 3
. Compiler doesn't need to call any operators in int
it just computes and stores the value at compile time.
it is same as short x = 3;
Here is the generated IL
IL_0001: ldc.i4.3 //Load the constant 3 into evaluation stack
IL_0002: stloc.0 // stores the value in stack to x
I've got no clue why this also works:
short x = (short)1 + (short)2;
The compiler evaluates the rhs expression at compile time and can prove that the result is within bounds.
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