Descriptor

Abstract type for descriptor-backed class fields.

Descriptor is not constructible directly.

Behavior

When a class body contains a member which is an instance of Descriptor, that field becomes descriptor-backed for all instances of the class.

For a descriptor-backed field obj.name:

reading obj.name calls descriptor.get(obj)
writing obj.name = value calls descriptor.set(obj, value)

Descriptor classification happens when the class is created. Assigning a descriptor object into an instance field later does not turn that field into a descriptor-backed field.

Methods

`get obj`

Returns the field value for obj.

Parameters:

Name	Type	Description
`obj`		instance being accessed

Returns: field value

`set obj value`

Updates the field value for obj.

Parameters:

Name	Type	Description
`obj`		instance being assigned
`value`		new field value

Returns: setter result

Example

class Twice: Descriptor
  pub def get self obj
    (obj.base * 2)

class Value
  pub let base = 21
  pub let doubled = Twice()

assert_eq $Value().doubled 42