Interface Instance<N>

Type Parameters:

N - the node type of the JSON model

All Known Implementing Classes:

Instance.LogicalInstance, Instance.NodesInstance, Instance.ValueInstance

public sealed interface Instance<N>
permits Instance.ValueInstance<N>, Instance.LogicalInstance<N>, Instance.NodesInstance<N>

An instance of a declared type: a function argument or a function result (RFC 9535, Section 2.4.1, Table 13).

Declared type	Record	Example of a source in a query
ValueType	Instance.ValueInstance	'text', @.price, length(@)
LogicalType	Instance.LogicalInstance	@.a == 1, match(@, 'a.*'), an existence test @.a
NodesType	Instance.NodesInstance	@.*, $..book

A FunctionExtension receives instances and gives an instance:

// first(NodesType): ValueType. The first node of a nodelist, or Nothing.
// A read-only extension: it runs with each JsonModel, also with a read-only model.
static final class First implements FunctionExtension {

    static final FunctionSignature SIGNATURE =
            new FunctionSignature("first", FunctionType.VALUE, List.of(FunctionType.NODES));

    @Override
    public FunctionSignature signature() {
        return SIGNATURE;
    }

    @Override
    public <N> Instance<N> apply(List<Instance<N>> arguments, JsonModel<N> model) {
        // The evaluator gives one instance for each parameter, of the declared type.
        List<Node<N>> nodes = ((Instance.NodesInstance<N>) arguments.getFirst()).nodes();
        // A ValueType result is an existing node, or Nothing.
        return new Instance.ValueInstance<>(nodes.isEmpty() ? Maybe.none() : Maybe.some(nodes.getFirst().value()));
    }
}

Nested Class Summary

Nested Classes

Modifier and Type	Interface	Description
static final record	Instance.LogicalInstance<N>	An instance of LogicalType: LogicalTrue or LogicalFalse.
static final record	Instance.NodesInstance<N>	An instance of NodesType: a nodelist.
static final record	Instance.ValueInstance<N>	An instance of ValueType: a node, or Nothing.