tomooda / Assertalk

Assertalk enables Smalltalk programs to define invariant assertions to instance variables. For example, with the following class defintion,

Object subclass: #SlotWithAssertionExample
    slots: { #value => SlotWithAssertion inv: [ :t | t isInteger ] }
    classVariables: {  }
    category: 'Assertalk-Tests'

assigning non-integer objects to the value will raise a SlotAssertionFailure exception.

value := 1.
self assert: [value = 1]
value := 'abc'.   "==> SlotAssertionFailure"

An erroneous assignment can be rolled back.

value := 1.
[value := 'abc'] on: SlotAssertionFailure do: [:ex | ex rollback].
self assert: [value = 1].