Pascal Function Overloading

What is Function Overloading?

In programming you may come across 2 or more functions that are named the same thing but act differently, wether thats taking in different types of arguments or different numbers of arguments. This is called function overloading. Some languages do not have this feature (such as JavaScript) but some do (such as Pascal).

Example

This program uses 3 different Add functions and the compiler will choose the correct one based on the arguments passed to it.

program FunctionOverloading;

uses
    SysUtils;

{$APPTYPE CONSOLE}

var
  intOut: Integer;
  realOut: Real;
  strOut: String;

function Add(const a, b: Integer): Integer; overload;
begin
  Result := a + b;
end;

function Add(const a, b: string): string; overload;
begin
  Result := a + b;
end;

function Add(const a, b: Double): Double; overload;
begin
  Result := a + b;
end;

begin
  intOut := Add(1, 2); // Integer overload
  realOut := Add(1.72, 2.525); // Real overload
  strOut := Add('Hello, ', 'world!'); // String overload

  WriteLn(Format('Int %d', [intOut]));
  // Int 3
  WriteLn(Format('Double %0.1f', [realOut]));
  // Double 4.2
  WriteLn(Format('String %s', [strOut]));
  // String Hello, world!

  Readln;
end.

The only thing needed to turn an function into an overloaded function is to add the overload keyword to the function declaration. The compiler will then know that this function is overloaded and will be able to choose the correct function based on the arguments passed to it. In this example we have 3 overloaded functions, one that takes in 2 integers, one that takes in 2 strings and one that takes in 2 doubles. The compiler will choose the correct function based on the arguments passed to it.

Use Cases

Function overloading is useful when you want to have multiple functions that do the same action but with different arguments, such as logging in with email, oAuth, phone number, etc. It would also be really useful for turning a variety of data types into a single one (possible a record) like a conversion or normalization.