Overloads in implementation

[aehimself 396]

Hello,

 

We just met a strange issue and was wondering if anyone can explain why it is happening. The below code throws a stack overflow, as the compiler doesn't make a difference between TDateTime and Integer and keeps calling the first method:

 

program Project1;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils,
  System.DateUtils;

function GetDay(dt: TDateTime): string; Overload;
begin
  Result := GetDay(DayOfTheWeek(dt));
end;

function GetDay(i: Integer): string; Overload;
const LDays: array[1..7] of string = ('H', 'K', 'S', 'C', 'P', 'S', 'V');
begin
  Result := LDays[I];
end;

begin
  WriteLn(GetDay(Today));
end.

It works perfectly if you turn it to a dummy class and publish these methods as class functions:

Type
  x = Class
    class function GetDay(dt: TDateTime): string; Overload;
    class function GetDay(i: Integer): string; Overload;
  End;

It also works if you push these two methods in a separate unit with proper Interface section:

unit Unit1;

interface

function GetDay(dt: TDateTime): string; overload;
function GetDay(i: Integer): string;  overload;

implementation

I guess it'll have something to do on how overloads are interpreted in the implementation area...? Delphi 10.4, 10.4.2 and 11 are producing the same symptom.

[Der schöne Günther 316]

The reason is that 

function GetDay(dt: TDateTime)

doesn't yet know about the other overload. You either have to replace their order or, better, add a definition like you did when you added their definition in the interface section of the unit.

Edited May 2, 2022 by Der schöne Günther

[Stefan Glienke 2002]

Nothing strange at all but standard pascal behavior - compiler only sees what has been declared so far.

 

 

Possible solutions:

- change implementation order

- declare in separate unit interface part

- use forward

[Fr0sT.Brutal 900]

I always try to declare methods so that most calls jump "up" (to the beginning of a unit).