zhelenskiy / KotlinRuntimeContracts

KotlinRuntimeContracts

This is a small library that provides runtime contracts.

Tests are attached

It supports:

• Using common () -> Boolean as contract
• Using Contract type
• Contract class:
  • Field name - name of the contract
  • Constructor that takes name of the contract, predicate checker and optional body string (can be used for composite contracts)
  • Method invoke (from () -> Boolean)
  • Readable .toString method (hierarchic structure representation) with given name
  • Open method why(interestInSuccess) that gives string representation only from that part of contract structure which leads to the asked result
    • It is just .toString by default
  • Method assertContract that checks if the the contract is fulfilled. If not so, the message why(false) is given as a description for the thrown ContractException
  • trueContract that is always fulfilled
  • falseContract that is never fulfilled
  • Static methods:
    1. all - takes contracts and returns contract that is fulfilled only if every parameter is fulfilled
    2. any - takes contracts and returns contract that is fulfilled only if at least 1 parameter is fulfilled
    3. none - takes contracts and returns contract that is fulfilled only if 0 parameters is fulfilled
    4. either - takes contracts and returns contract that is fulfilled only if exactly 1 parameter is fulfilled
    5. infix leadsTo - takes two contracts and returns a contracts that checks that if precondition is fulfilled, then postcondition is correct too.
    6. not - takes a contract and returns a contract with negated condition of success
  • Interface Contracted
    • Indicates that class has invariant contract.
  • Extension method T.checkClassContract that check contract of the object if it is Contracted
• Examples:

  • all({ a % 2 == 0}, { b == 0 } leadsTo { a == null })

  • all(Contract("Length is even") { a % 2 == 0}, { b == 0 } leadsTo { a == null }) 

  • either(
        not { coll is RandomAccess },
        Contract ("Some strange condition") {
            when (a) {
                a is Int -> a + 1 < 100
                a is String -> a.length < 100
                else -> true
            }
        }
    )

• .toString output of the prelast example when a = 1, b = 2

  [FALSE]
  All {
  	[FALSE]
  	Length is even
  	[TRUE]
  	Conditional {
  		:Pre
  		[FALSE]
  		<Predicate>
  		   |
  		   V
  		:Post
  		[FALSE]
  		<Predicate>
  	}
  }

• .why(false) output of that example

  [FALSE]
  All {
  	[FALSE]
  	Length is even
  }

• .why(true) output of that example

  [FALSE]
  All