Intrinsic for type of integer

[Okoba]

Hello,

I know I can use GetTypeKind Intrinsic to get the type of a variant, but it returns tkInteger for many integer types. I can use SizeOf Intrinsic to detect the size, so I can find out the difference of Integer and Byte for example.
But how can I detect the difference between Byte and Shortint? Their both size is 1.
I want Intrinsic as I like my function to solve in compile time.

Code: Pascal  [Select][+][-]

1. program Project1;
2.  
3.   {$mode delphi}
4.  
5.   procedure Test<T>(V: T);
6.   begin
7.     if GetTypeKind(V) = tkInteger then
8.       case SizeOf(V) of
9.         1: WriteLn('Byte or Shortint?');
10.         4: WriteLn('Integer');
11.       end;
12.   end;
13.  
14. begin
15.   Test<Integer>(1);
16.   Test<Byte>(1);
17.   Test<Shortint>(-1);
18.   ReadLn;
19. end.        

[jamie]

I don't know what you are trying to do but you always have the "TValueType" enum to play with.

[Okoba]

What is "TValueType"?

[cdbc]

Hi
I think @jamie: means "system.TTypeKind"...
...and for that you can use "system.TypeInfo()", it returns a record with Name & Type = PTypeInfo; { uses typinfo; }
Regards Benny

[Okoba]

TTypeKind is what I am already using. But it does not let you know if that is for example a Byte or a Shortint!

[Kays]

[…] But how can I detect the difference between Byte and Shortint? Their both size is 1. […]

You cannot determine it at compile-time. You do it dynamically. The signed ranges are preferred. So a one byte integer quantity that has a value ≤ +127 is an int8, otherwise a Byte.

Code: Pascal  [Select][+][-]

1.         4: WriteLn('Integer');

It’s longInt or longWord.

[cdbc]

Hi
Sorry mate, sloppy of me 
Regards Benny

[Okoba]

No problem @cdbc, and thank you.
Thank you @Kays.

That is a shame for a type safe language, that it does not even exposes the types properly.

[bytebites]

High(V) tells if it is signed or not

[jamie]

I suppose you have looked at TVarData ? That uses Variants and requires the variants unit to be used.

TVarData does have all of those as types.

But of course, you won't like using them because of the size of record.  For me, Its a great when using them via reference.

[Warfley]

The problem is, you are attempting to do meta programming on those types by mixing runtime code (if-thrn-else) on compiletime information. This is not that well supported in FPC, as usually compiletime and runtime information are quite seperated

What you can do is to resolve type information fully at compiletime using compile time polymorphism through function overloading:

Code: Pascal  [Select][+][-]

1. TIntType = (u8, s8, ...);
2.  
3. function IntType(AInt: Byte): TIntType; overload; inline;
4. begin
5.   Result := TIntType.u8;
6. end;
7.  
8. function IntType(AInt: SmallInt): TIntType; overload; inline;
9. begin
10.   Result := TIntType.s8;
11. end;
12.  
13. // use
14. var
15.   B: Byte;
16. begin
17.   WriteLn(IntType(b)); // shows u8

Here the compiler will map your types to results through resolving the overloaded function. Through inlining no extra code should be generated

[Okoba]

@Warfley your way seems great! Thank you.
Mixing if then with compile time code is not well supported, yes. But for type oriented task like generic functions, it is very useful.

[Wallaby]

Use TypeInfo and check against the types you want. Sample:

Code: Pascal  [Select][+][-]

1. program Project1;
2.  
3.   {$mode delphi}
4.  
5.   procedure Test<T>(V: T);
6.   begin
7.     if TypeInfo(V) = TypeInfo(Integer) then
8.       WriteLn('Integer')
9.     else
10.     if TypeInfo(V) = TypeInfo(Byte) then
11.       WriteLn('Byte')
12.     else
13.     if TypeInfo(V) = TypeInfo(Shortint) then
14.       WriteLn('Shortint')
15.     else
16.       WriteLn('Something else');
17.   end;
18.  
19. begin
20.   Test<Integer>(1);
21.   Test<Byte>(1);
22.   Test<Shortint>(-1);
23.   Test<LongWord>(-1);
24.   ReadLn;
25. end.

This will print

Code: Text  [Select][+][-]

1. Integer
2. Byte
3. Shortint
4. Something else

[Okoba]

@Wallaby that is an even better way! Thank you.
Although Test needs inline otherwise it will not resolve on compile time.