Constructors and Free in Delphi

A booking built by a constructor that takes arguments, then freed in a finally block.

program ConstructorFree;
uses SysUtils;
type
  TBooking = class
    Summary: string;
    constructor Create(const AGuest: string; ANights: Integer);
  end;
constructor TBooking.Create(const AGuest: string; ANights: Integer);
begin
  Summary := Format('%s: %d nights', [AGuest, ANights]);
end;
var Stay: TBooking;
begin
  Stay := TBooking.Create('Rivera', 3);  // whoever calls Create owns it
  try
    WriteLn(Stay.Summary);
  finally
    Stay.Free;  // and the owner frees it, on every way out of the block
  end;
end.

How it works

1. constructor Create(const AGuest: string; ANights: Integer) takes the values the object needs.
2. The body fills the field with Format('%s: %d nights', [AGuest, ANights]).
3. Stay := TBooking.Create('Rivera', 3) makes the caller the owner, so Stay.Free sits in finally.

Keywords and builtins used here

• Create
• Format
• Integer
• TBooking
• WriteLn
• begin
• class
• const
• constructor
• end
• finally
• program
• string
• try
• type
• uses
• var

The run, in numbers

Lines

20

Characters to type

489

Tokens

101

Three-star pace

70 tpm

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Type this snippet

Step 3 of 3 in Classes, step 21 of 27 in Language basics.

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