Eugine Savin

On 2/27/2024 at 11:00 PM, Ali Dehban said:

It seems using RTTI's TValue it is possible to handle this situation somehow.

You can do it without TValue

if TypeInfo(T) = TypeInfo(Integer) then PInteger(@Result)^ := 10

else if TypeInfo(T) = TypeInfo(string) then PString(@Result)^ := 'Hello'

Ha, delphi 10.4 has a bug here. 

type
iSomeInterface<T> = interface

end;
Type tSomeclass<T:iInterface>=CLass (tInterfacedObject, iSomeInterface<T>)
     Constructor Create(s: string);
     Function CreateNewInstance:iSomeInterface<T>;
  end;


  Function tSomeclass<T>.CreateNewInstance:iSomeInterface<T>;
  type
    TSelfClass = tSomeclass<T>;
    TSomeClassType = class of TSelfClass; // !!!!!!!!!!!! [dcc32 Error] Unit9.pas(36): E2021 Class type required
  begin
      result:=TSomeClassType(Self.Classtype).Create('s'); //Does not compile
  end;

cCircleZero: TCircle = (C: (x: 0; y: 0); Radius: 0.0);

Current output is 'ne', I think, it's a bug. If I explicitly set type of variable B to Currency - output will be 'eq' as expected. I use Delphi 10.4 (also please check this code in Delphi 11)

program Project3;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils;

  function GetCurrency: Currency;
  begin
    Result := 8.52;
  end;

var
  A: Currency;
begin
  A := GetCurrency;
  //var B: Currency := GetCurrency();  // 1
  var B := GetCurrency(); // 2
  if A = B then WriteLn('eq') else WriteLn('ne');
  ReadLn;
end.

Oh, sorry, my fault, I believe that I have similar code but it does not have generic constraints. Perhaps I ran into this issue earlier, but forgot about it

As least Delphi Tokio compiles this code successfully

if I pass set type into MyGenericMethod<T: record> - I get compile type error [dcc32 Error] Project2.dpr(28): E2512 Type parameter 'T' must be a non-nullable value type

Is it OK or compiler bug ??

program Project2;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils;


type
  TMyEnum = (en1);
  TMySet = set of TMyEnum;

type
  TTestClass = class
    class procedure MyGenericMethod<T: record>;
  end;

class procedure TTestClass.MyGenericMethod<T>;
begin
//
end;

begin
  try
    { TODO -oUser -cConsole Main : Insert code here }
    TTestClass.MyGenericMethod<TMySet>();
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.

class function TNumbers.FromInteger<T>(AValue: Integer): T;
type
  PSingle = ^Single;
begin
  if TypeInfo(T) = TypeInfo(Single) then PSingle(@Result)^ := AValue
  else if TypeInfo(T) = TypeInfo(Integer) then PInteger(@Result)^ := AValue
  else raise Exception.Create('Error Message');
end;

type
  TNumbers = class
  public
    class function One<T>: T;
  end;

{ TNumbers }

const
  OneSingle: Single = 1;
  OneInteger: Integer = 1;
class function TNumbers.One<T>: T;
type
  PT = ^T;
begin
  if TypeInfo(T) = TypeInfo(Single) then Result := PT(@OneSingle)^
  else if TypeInfo(T) = TypeInfo(Integer) then Result := PT(@OneInteger)^
  else raise Exception.Create('Error Message');
end;
  
...
FPen.Width := TNumbers.One<T>;

https://bitbucket.org/sglienke/spring4d/src/ffee3360a2e8cb9ae5311621a745bb9ed809870f/Source/Base/Spring.pas#lines-956

?

This shouldn't work. Make method Test virtual and override it in Test2

1 minute ago, Rudy Velthuis said:

How would you do this in, say, C++?

In C++ there is not differences between functions and overloaded operators.

struct MyArray {
public:
    template <std::size_t N>
    bool operator==(int (&rhs)[N]) { std::cout << N << '\n'; return true; }
};

int main() {
    // your code goes here
    int arr1 [1] = {0};
    int arr2 [2] = {0, 0};
    MyArray myArr;
    if (myArr == arr1 && myArr == arr2) {}
    return 0;
}

20 minutes ago, Rudy Velthuis said:

And don't use operators.

Can you explain why you allow operators with dyn arrays, and do not allow ones with open arrays ?

1 minute ago, Rudy Velthuis said:

it doesn't make sense to give operators open array parameters.

TMyArray = record
..
end;

const Arr1: array[0..1] of Integer = (..)
const Arr2: array[0..2] of Integer = (..)
var MyArray: TMyArray ..

I wanna have ability to compare if (MyArray == Arr1) or (MyArray = Arr2)..   How can I get it without open arrays as operator parameters ?

1 minute ago, Rudy Velthuis said:

But not open array arguments, IMO

What's problems with open arrays ? Anyway if I replace "array of Integer" by "TArray<Double>"  r * [10.0] - compiled, but r = [10.0] is not ( E2001 Ordinal type required)

// qc link https://quality.embarcadero.com/browse/RSP-23498

And main question, why 

r := r * [10] // here [10] is array

and

b := r = [10] // here [10] is set

what's difference ??

44 minutes ago, Uwe Raabe said:

because in the second case "[10]" is seen as a set constant by the compiler

Well, where is not "set of Integer", but code

var i: Integer;
begin
  i := 10;
  b := r = [i];
end

is not compiled

Simple question, why "Multiply" operator works, and "Equal" does not. compiler give error  "[dcc32 Error] Project1.dpr(33): E2015 Operator not applicable to this operand type"

program Project1;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils;

type
  TMyRecord2 = record
  public
    class operator Equal(const a: TMyRecord2; const b: array of Integer): boolean;
    class operator Multiply(const a: TMyRecord2; const b: array of Integer): TMyRecord2;
  end;

class operator TMyRecord2.Equal(const a: TMyRecord2; const b: array of Integer): boolean;
begin
  Result := True;
end;

class operator TMyRecord2.Multiply(const a: TMyRecord2; const b: array of Integer): TMyRecord2;
begin
  Result := a;
end;

var
  b: boolean;
  r: TMyRecord2;
begin
  try
    r := r * [10]; // this line is compiled
    b := r = [10]; // this line is not compiled
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.