Readonly (keyword)

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The readonly keyword is used to create fields that are read-only from any place outside the constructor (or class constructor). These fields therefore are immutable and are useful when writing thread-safe classes. Instead of changing the values of the fields on immutable classes, new classes are created with the new values.

The "readonly" directive

type
  MyClass = class
    var i: Integer; readonly;
    ...
  end;

Readonly classes

type
  ImmutableClass = public readonly class
  public 
    property Name: string;
    property Address: string;
    constructor(aName, anAddress: string);
  end;


constructor ImmutableClass(aName, anAddress: string);
begin
  Name := aName;
  Address := anAddress; 
end;

Adding the readonly keyword to a class makes all fields and properties with implicit fields read-only. They can only be set from the constructor. This feature aids in writing immutable classes.

Applies to

• Properties
• Fields
• Classes

See Also

• Classes
• Class Members
• Class Member Modifiers

Area: Oxygene Language
Compiler version: Oxygene 5

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