Properties

• What properties are and aren't
• Simple properties
• Virtual properties
• Differing qualifiers
• Indexed properties
• Self properties
• Delegates and properties
• Watch out for the combination of indexed and default properties
• Overloaded properties

What properties are and aren't

While properties may look like commands and functions, they aren't. A property shouldn't be used unless directly backed by a member. So if a string property call MyStringProperty is present, you should have a string member called MyString in the same scope. The exception is properties that have only a get accessor. They might be used to compute something. However, all get accessors are implicitly constant as though they were declared with the const keyword.

Simple properties

Properties in ASIL are most similar to those in C#, but are more flexible. Think of the get clause as a function and the set clause as a command. Each clause is a type of procedure called an "accessor".

A simple property:

public property String MyProperty
  get
    return "a"

  set
    someMember = value

Note: Unlike functions, a property can be called either the get or the set accessor, but not both in a single call. In the code below, ASIL would call the set accessor , but not the get accessor. Instead, ASIL would pass the string constant to whatever S$ turned out to be.

S$ = MyProperty = "5sdf"

Virtual properties

A property can be virtual and shown below. If you're overriding such a property, you need to use the override keyword.

public virtual property IntProperty%
  get
    return 3

  set
    intMember% = value

Differing qualifiers

The get and set accessors can have different access qualifiers. You can also make one final and one virtual if needed. Whatever is given for the property applies for the accessors unless they override it.

public property NewProp#
  virtual get
    return null

  final set
    test# = value

Indexed properties

Unlike C#, ASIL properties can be indexed and take parameters. These parameters are calleed "index parameters". Your property must take the same index parameters for both the get and set accessors. If you need different versions, consider overloading. If the type you're returning has the self property, your property takes precedence. Custom keywords are allowed. The brackets are required. Those in the declaration below don't mark an optional sequence, but are how you specify the property is indexed.

public property boolean IsReady[var int index]
  get
    return i[index]

  set
    i[index] = value

You call an indexed property like this:

if IsReady[4] then
  IsReady[3] = true

Self properties

You can have a property on the self keyword. This is called a default property. It is always indexed.

public property byte self[var String strName]
  get
    return map.lookupName strName

This is how you call it:

instance["name"]

Delegates and properties

See [Delegates] on how to create delegates for properties.

Watch out for the combination of indexed and default properties

Examine the code below.

class MyClass
  public property int self[var int index]
    get
      ' return some value

class OtherClass
  public property MyClass Prop[var int index]
    get
       ' return some value

Now look at this code:

var OtherClass myOtherClass = new OtherClass ' Presumably we declared constructors for both classes

var int i% = myOtherClass.Prop[7] ' Error as OtherClass.Prop returns a MyClass
var int j% = myOtherClass.Prop[7][4] ' Valid as the "[4]" portion is the default property

Overloaded properties

ASIL allows properties to be overloaded. However, all the overloads must be of the same type. You will need at least one to be indexed, unless the property is the default property, in which case all the overloads will be indexed.