The WhenFalse() method is used to yield values when the proposition is unsatisfied. It also implicitly sets TMetadata type for the rest of the proposition. Any values yielded from underlying propositions (if they exist) will be supplanted by the new value from the WhenFalse() method. However, should the underlying yielded values still be required, then it is still possible to re-yield them.

Whilst the WhenFalse() method overloads remains broadly consistent across the various ways a proposition can be built, there are nuances to be aware of that are as a result of prior builder method calls. The outliers are the Higher-Order propositions, which require the pairing of models and results to be preserved for them to be useful, and atomic propositions that have no underlying propositions to yield assertions/metadata from.

This method is overloaded and takes one of the following types

Type	Description
string	a fixed assertion statement.
TMetadata	a fixed metadata value.
Func<TModel, string>	a factory function that returns an assertion statement.
Func<TModel, TMetadata>	a factory function that returns a metadata value.
Func<TModel, BooleanResultBase<TMetadata>, string>	a factory function that returns an assertion statement.
Func<TModel, BooleanResultBase<TMetadata>, TMetadata>	a factory function that returns a metadata value.

Fixed assertion

WhenFalse(string assertion)

This overload generates an assertion statement when the proposition is not satisfied. When the proposition is not satisfied, the assertion will be used to populate the Reason, Assertions and Metadata properties of the result.

Spec.Build((int n) => n % 2 == 0)
    .WhenTrue("is even")
    .WhenFalse("is odd")
    .Create();

Fixed metadata

WhenFalse(TMetadata metadata)

This overload generates a metadata value when the proposition is not satisfied. When the proposition is not satisfied, the metadata returned by the factory function will populate the Metadata property of the result.

Spec.Build((int n) => n % 2 == 0)
    .WhenTrue(new MyMetadata("is even"))
    .WhenFalse(new MyMetadata("is odd"))
    .Create("is even");

Dynamic assertion (derived from model)

WhenFalse(Func<TModel, string> factory)

This overload generates an assertion statement based on the model when the proposition is not satisfied. When the proposition is not satisfied, the metadata returned by the factory function will be used to populate the Reason, Assertions and Metadata properties of the result.

Spec.Build((int n) => n % 2 == 0)
    .WhenTrue("is even")
    .WhenFalse(n => $"{n} is odd")
    .Create();

Dynamic metadata (derived from model)

WhenFalse(Func<TModel, TMetadata> factory)

This overload generates a metadata value based on the model when the proposition is not satisfied. When the proposition is not satisfied, the metadata returned by the factory function will populate the Metadata property of the result.

Spec.Build((int n) => n % 2 == 0)
    .WhenTrue(new MyMetadata("is even"))
    .WhenFalse(n => new MyMetadata($"{n} is odd"))
    .Create("is even");

Extra usages when building upon existing propositions or results

Dynamic assertion (derived from model and underlying result)

WhenFalse(Func<TModel, BooleanResultBase<TMetadata>, string> factory)

This overload generates an assertion statement based on the model and the result of the underlying proposition. When the proposition is not satisfied, the metadata returned by the factory function will be used to populate the Reason, Assertions and Metadata properties of the result.

Spec.Build(new IsEvenProposition())
    .WhenTrue("is even")
    .WhenFalse((n, result) => result.Assertions.Serialize())
    .Create();

Dynamic metadata (derived from model and underlying result)

WhenFalse(Func<TModel, BooleanResultBase<TMetadata>, TMetadata> factory)

This overload generates a metadata value based on the model and the result of the underlying proposition. When the proposition is not satisfied, the metadata returned by the factory function will populate the Metadata property of the result.

Spec.Build(new IsEvenProposition())
    .WhenTrue(new MyMetadata("is even"))
    .WhenFalse((n, result) => new MyMetadata($"{n} {result.Reason}"))
    .Create("is even");

Extra usages when building a higher-order proposition

Dynamic assertion (derived from pairwise models and results)

WhenFalse(Func<HigherOrderBooleanEvaluation<TModel>, string> factory)

This overload generates an assertion statement based on the pairwise models and results when the proposition is not satisfied. When the proposition is not satisfied, the metadata returned by the factory function will be used to populate the Reason, Assertions and Metadata properties of the result.

Spec.Build((int n) => n % 2 == 0)
    .AsAllSatisfied()
    .WhenTrue("is even")
    .WhenFalse(eval => $"{eval.CausalModels.Serialize()} are odd")
    .Create();

Dynamic metadata (derived from higher-order evaluations)

WhenFalse(Func<HigherOrderBooleanEvaluation<TModel>, TMetadata> factory)

This overload generates a metadata value based on the pairwise models and results when the proposition is not satisfied. When the proposition is not satisfied, the metadata returned by the factory function will populate the Metadata property of the result.

Spec.Build((int n) => n % 2 == 0)
    .AsAllSatisfied()
    .WhenTrue(new MyMetadata("is even"))
    .WhenFalse(eval => new MyMetadata($"{eval.CausalModels.Serialize()} are odd"))
    .Create("is even");