Type result with conditional operator in C?

The compiler does not infer the type of the result of the conditional operator from the usage of the result, but from the types of its arguments. The compiler fails when it sees this expression because it cannot deduce the type of the result: IsDateTimeHappy(myDateTime)? Null : myDateTime Since null and DateTime are not compatible, you need to tell the compiler what the type should be.

A cast should do the trick: DateTime? X = IsDateTimeHappy(myDateTime)? (DateTime?)null : myDateTime; OutputDateTime(x) Now the compiler will have no problems.

You can also write the above on one line if you prefer (but I would probably not do this): OutputDateTime(IsDateTimeHappy(myDateTime)? (DateTime?)null : myDateTime) Eric Lippert has a good answer that is also relevant here and goes into more details about how the compiler determines types.

The compiler does not infer the type of the result of the conditional operator from the usage of the result, but from the types of its arguments. The compiler fails when it sees this expression because it cannot deduce the type of the result: IsDateTimeHappy(myDateTime)? Null : myDateTime; Since null and DateTime are not compatible, you need to tell the compiler what the type should be.

A cast should do the trick: DateTime? X = IsDateTimeHappy(myDateTime)? (DateTime?)null : myDateTime; OutputDateTime(x); Now the compiler will have no problems.

You can also write the above on one line if you prefer (but I would probably not do this): OutputDateTime(IsDateTimeHappy(myDateTime)? (DateTime?)null : myDateTime); Eric Lippert has a good answer that is also relevant here and goes into more details about how the compiler determines types.

MyDateTime = DateTime. Now; – Nathan Ernst May 11 '10 at 23:50.

The implicit conversion is not allowed by the return statement. If you had if (condition) return first_expression; else return second_expression; Then you'd be comparing apples to apples. And you'd have no problems - as you stated.In your case, you're allocated so much space on the stack for a DateTime - which is a non-nullable value type.

So you're making a statement that doesn't make any sense to the compiler. If you say, I'm going to pass you an A or a B, then the A and the B need to be the same thing.In your case, the B can never be an A.

I think this is also answered here: stackoverflow.com/questions/858080/nulla... Hope that's what you needed. =.

The reason is the ternary operator expects both the operands to be of the same type. The whole operator get worked out BEFORE it is assigned to a result (in this case passed into a function), so the compiler can't know what the result type is. IsDateTimeHappy(myDateTime)?

Null : myDateTime In the above case there is no conversion path between null and DateTime. As soon as you cast one of them to DateTime? , the compiler can convert the other one: IsDateTimeHappy(myDateTime)?(DateTime?)null : myDateTime //OR IsDateTimeHappy(myDateTime)?

Null : (DateTime? )myDateTime The fist line of code above works because the compiler can convert DateTime to DateTime? Via an implicit conversion operator: //In Nullable public static implicit operator T?(T value); The second line works because null can be assigned to DateTime?

Since the latter is a reference type.

What the compiler is saying is: If IsDateTimeHappy(myDateTime) is false, then I need to return a value of type DateTime equal to myDateTime. If it is true, then I need to return a value equal to null, but you haven't told me what type it should be! That's why Mark's answer is the solution.

After you provide a cast telling the compiler what type of value will be returned if the condition is true, it can check whether the true and false return values can be converted to (or are of) the same type. Cheers Mark! ;-).

And then both sides of the ternary will have compatible types.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.