Error casting object? to int.

[AlfonsByRecognize]

We have the following code:

	uint noproblem = (uint) 32;
	int noproblemresult = (int) noproblem;
	
	object? test = (uint) 32;
	int result = (int) test;

The first 2 lines doesnt throw an error, the 2nd 2 lines throw 'Unable to cast object of type 'System.UInt32' to type 'System.Int32''. Can someone explain me why?

[CyrusNajmabadi]

The bottom example is a runtime cast. And Because a uint is not an int, the runtime fails to cast.

The top example, is not a runtime-cast. It is a "c# conversion", and c# has special rules on what to do here when the types are statically known.

[bernd5]

Is it really the case?
I thought uint to int conversion is simply a reinterpretation of the bytes (outside of an checked environment) - that is the reason why no code for that is emitted. But both conversions are runtime conversions.

The actual problem is that the runtime does not unboxing + value type conversion.

So you would need to write:

object? test = (uint) 32;
int result = (int)(uint) test; //first unbox then convert

[HaloFour]

I thought uint to int conversion is simply a reinterpretation of the bytes (outside of an checked environment)

That would be the C# conversion aspect of it.

[huoyaoyuan]

Casting from object to value type is unboxing. It's a different type of cast than numeric casting. C# doesn't use C++-style cast operators to distinguish different casts, but only uses C-style casts.