CODEWITHSUNDEEP
delphigenericsinteger
Alexandre
Alexandre

Reputation: 507

Delphi Generic Types - Specificity?

I am trying to create a generic class under delphi called TRange. The idea is that it can be a Range of Integer or a range of single, or Double, etc...

The TRange object contains a few variables of type T (maxValue, minValue, idealValue, etc). The TRange contains a function for each of them to convert them into a string. However, since Delphi is a strong-typed language, I need to specify "How-To" convert the different variables into a string.

I can get the typeName of the T type using GetTypeName (TypeInfo (T)). Once I know which type is T, I thought I could do something like:

if(className = 'single') then
 result := formatFloat('0.0', self.AbsMin as Single)
 else
 result := intToStr(self.AbsMin as Integer)

However, the compiler tells me "Operator not Applicable to this operand Type".

So, I guess my question is :

Is there a way to give specificity to a generic Class???

Upvotes: 2

Views: 765

Answers (1)

jpfollenius
jpfollenius

Reputation: 16620

The compiler error comes from the fact that you cannot use the as operator to cast to a primitive type such as Single or Integer. Use a hard cast for that: Single(AbsMin).

Is there a way to give specificity to a generic Class???

Why do you need to convert the values to strings? This is kind of against the idea of a generic class, because you are now back to implementing special behaviour for all the cases.

If you really need this though you could introduce an interface

IValueStringConverter <T> = interface
  function ToString(Value : T) : String;
end;

You can just supply the converter in the constructor of the TRange class and store it in a field:

constructor TRange <T>.Create(Converter : IValueStringConverter <T>);
begin
FConverter := Converter;
end;

Now just use the converter inside the class to do the conversion:

Str := FConverter.ToString(AbsMin);

Upvotes: 6

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