Add hasValue function to Nullable

[kick martens]

Hi,

Could you add a function hasValue to the Nullable<T> type? It should be the opposite of isNull. It is so much more readable to write: if someVar.hasValue and otherVar.hasValue then doSomething(someVar.value, othervar)

instead of if (not somevar.isnull) and (not othervalue.isnull) then

[Stefan Glienke]

I think you are confusing something. Nullable<T> has no property called IsNull but only the HasValue property.

[kick martens]

I am sorry, you are right. I meant adding an isNull method ;-) I manually added it and mixed up what was the original one. It seems redundant but having both functions makes code more readable instead of using "not"

[Stefan Glienke]

By that argumentation you could duplicate every boolean property ("Hey, you have Enabled, can you please Disabled which is the opposite? And while at it please also add Inactive and Invisible") ;)

Also by the code you showed I cannot imagine many places where you explicitly check for IsNull than rather for HasValue given that you have functions like GetValueOrDefault where you can provide a value in case the nullable does not contain one.

[kick martens]

By that argumentation you could duplicate every boolean property You have point there. Still "isNull" for a nullable seems a logical method to call.

Also by the code you showed I cannot imagine many places where you explicitly check for IsNull than rather for HasValue I do have a lot of code where the value of properties is replaced by something else when property itself is null. I am currently porting this code from TMS Aurelius to the Spring4D framework. The Nullable<T> of Aurelius does have both 'isNull' and 'hasValue', so I added it to the Spring4D Nullable<T> to make my live easier. I guess I will have to refactor the code to make it only use hasValue.

[kick martens]

sorry, I duplicated your responses, but the post stripped some of the formatting

[Stefan Glienke]

What does the code typically look like when it uses if someVar.IsNull then?

[kick martens]

My object has a property Inkoopkorting (discount), when it is set (has a value) I want to use its value, otherwise I calculate the value using other properties. My code is full of this kind of constructs. I could refactor them, and it would be equally readable to be honest, it's just a lot work ;-)

function TBasisRegel.GetInkoopkorting: Single; 
begin 
  if FInkoopkorting.IsNull then 
  begin 
     if (FBrutoInkprijs.ValueOrDefault<>0) and FNettoInkprijs.HasValue then 
        result := (1-(FNettoInkprijs.Value/FBrutoInkprijs.value))*100 
     else 
       result := 0; 
   end else 
     result := FInkoopkorting.value; 
end;

I could refactor to

if FInkoopkorting.hasvalue then 
   result := FInkoopkorting.value 
else 
begin 
  if (FBrutoInkprijs.ValueOrDefault<>0) and FNettoInkprijs.HasValue then 
    result := (1-(FNettoInkprijs.Value/FBrutoInkprijs.value))*100 
  else 
    result := 0; 
end

I went through my code and the more complex if statements all use hasvalue. So it would make more sense to have a hasValue if you could have only one. So forget I asked, I will refactor my Aurelius code so I only use hasvalue.

[Stefan Glienke]

It's just reversing the true and false branch of the if statement then.

FWIW you can also write this:

if not FInkoopkorting.TryGetValue(Result) then 
begin 
  if (FBrutoInkprijs.ValueOrDefault<>0) and FNettoInkprijs.HasValue then 
    result := (1-(FNettoInkprijs.Value/FBrutoInkprijs.value))*100 
  else 
    result := 0; 
end

I will close this as won't fix. I think for migrating your code it might be helpful to add the IsNull property and keep or refactor later. But imo there is no reason to add it to the library.