.InvariantsCoreAbstractInvariant

			abstract type AbstractInvariant

An Invariant checks if an input satisfies some invariant. For example, it may check whether a number is positive.

For most use cases, using invariant to create an invariant will suffice and implementing your own subtype of AbstractInvariant will rarely be necessary.

The interface of Invariant s is designed so that

• the invariant can be checked, given some input

• invariants can be composed to generate more complicated invariants

• the creation of rich error messages is possible when an invariant is not satisfied.

Interface

An Invariant I must implement the following methods:

• title (::I)::String : Descriptive name for the invariant

• description (::I)::String : A longer description of the invariant, giving explanation and pointing to related information.

• satisfies (::I, input) -> (nothing | msg) : Check whether an input satisfies the invariant, returning either nothing on success or an error message.