context-parameters.md

icon	description
nfc-magnifying-glass	Context resolvers allow for dynamic resolution of context-specific values into command parameters, enabling commands to adapt based on the environment or actor state.

Context parameters

Overview

ContextParameter is a functional interface that allows you to resolve parameters based on the context of the command execution. This can be useful for extracting complex types or values from the command context.

ContextParameter Interface

The ContextParameter interface is used to define how a parameter should be resolved from the command context.

@FunctionalInterface
public interface ContextParameter<A extends CommandActor, T> {

    /**
     * Reads input from the given {@link MutableStringStream}, parses the object, or throws
     * exceptions if needed.
     *
     * @param parameter The parameter
     * @param context   The command execution context, as well as arguments that have been resolved
     * @return The parsed object. This should never be null.
     */
    T resolve(@NotNull CommandParameter parameter, @NotNull ExecutionContext<A> context);
}

ContextParameter.Factory Interface

The ContextParameter.Factory interface is used to create ContextParameter instances dynamically. It is helpful for creating custom parameter types.

@FunctionalInterface
public interface ContextParameter.Factory<A extends CommandActor> extends ParameterFactory {

    /**
     * Dynamically creates a {@link ContextParameter}
     *
     * @param <T>           The parameter type
     * @param parameterType The command parameter to create for
     * @param annotations   The parameter annotations
     * @param lamp          The Lamp instance (for referencing other parameter types)
     * @return The newly created {@link ContextParameter}, or {@code null} if this factory
     * cannot deal with it.
     */
    @Nullable
    <T> ContextParameter<A, T> create(@NotNull Type parameterType, @NotNull AnnotationList annotations, @NotNull Lamp<A> lamp);
}

Example: PlayerWorldContextParameterFactory

Here is an example of a ContextParameter.Factory that resolves a World from the Player context:

{% tabs %} {% tab title="Java" %}

public class PlayerWorldContextParameterFactory implements ContextParameter.Factory<BukkitCommandActor> {

    @Nullable
    @Override
    public <T> ContextParameter<BukkitCommandActor, T> create(@NotNull Type parameterType, @NotNull AnnotationList annotations, @NotNull Lamp<BukkitCommandActor> lamp) {
        if (parameterType != World.class) {
            return null;
        }
        PlayerWorld playerWorldAnnotation = annotations.get(PlayerWorld.class);
        if (playerWorldAnnotation == null) {
            return null;
        }
        return (parameter, context) -> context.actor().sender().requirePlayer().getWorld();
    }
}

{% endtab %}

{% tab title="Kotlin" %}

object PlayerWorldContextParameterFactory : ContextParameter.Factory<BukkitCommandActor> {

    @Suppress("UNCHECKED_CAST")
    override fun <T> create(parameterType: Type, annotations: AnnotationList, lamp: Lamp<BukkitCommandActor>): ContextParameter<BukkitCommandActor, T>? {
        if (parameterType != World::class.java) {
            return null
        }
        val playerWorldAnnotation = annotations.get(PlayerWorld::class.java)
        if (playerWorldAnnotation == null) {
            return null
        }
        return ContextParameter { _, context -> context.actor().sender().requirePlayer().world } as ContextParameter<BukkitCommandActor, T>
    }
}

{% endtab %} {% endtabs %}

Registering ContextParameter.Factory

You can register a ContextParameter.Factory with the Lamp builder to handle custom parameter types.

{% tabs %} {% tab title="Java" %}

var lamp = BukkitLamp.builder(this)
    .parameterTypes(parameters -> {
        parameters.addContextParameterFactory(new PlayerWorldContextParameterFactory());
    })
    .build();

{% endtab %}

{% tab title="Kotlin" %}

val lamp = BukkitLamp.builder(this)
    .parameterTypes { parameters ->
        parameters.addContextParameterFactory(PlayerWorldContextParameterFactory())
    }
    .build()

{% endtab %} {% endtabs %}