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Class PolymorphicAction<T>

A decorator to enable subtype polymorphism for action classes.

By convention, concrete action subclasses are named with verb phrases, e.g., Heal, Sell.

One downside of this compared to the vanilla IAction is the fact that it uses reflection under the hood. This may cause compatibility issues on certain platforms, and is slightly slower.

Inheritance
Object
PolymorphicAction<T>
Implements
IAction
Inherited Members
Object.Equals(Object)
Object.Equals(Object, Object)
Object.GetHashCode()
Object.GetType()
Object.MemberwiseClone()
Object.ReferenceEquals(Object, Object)
Object.ToString()
Namespace: Libplanet.Action
Assembly: Libplanet.dll
Syntax
public sealed class PolymorphicAction<T> : IAction where T : IAction
Type Parameters
Name Description
T

An action base class which implements IAction and has subclasses. Usually an abstract class.

Remarks

Every concrete action subclass of T has to be marked with the ActionTypeAttribute. Even if a superclass is marked with the ActionTypeAttribute its subclass also should be marked with the ActionTypeAttribute if it is concrete.

Examples

The following example shows how polymorphic actions look like (compare this with an IAction example without subtype polymorphism):

using System;
using System.Collections.Immutable;
using Libplanet;
using Libplanet.Action;

// Instead of having multiple in-game actions in a class,
// in this example, we declare one abstract base class
// and its three concrete subclasses.
public abstract class ActionBase : IAction
{
    public ActionBase() { }

    public ActionBase(Address targetAddress)
    {
        TargetAddress = targetAddress;
    }

    public Address TargetAddress { get; private set; }

    // Leaves Execute() abstract so that concrete subclasses
    // implement their own logic.
    public abstract IAccountStateDelta Execute(IActionContext context);

    IImmutableDictionary<string, object> IAction.PlainValue =>
        ImmutableDictionary<string, object>.Empty
            .Add("target_address", TargetAddress);

    void IAction.LoadPlainValue(
        IImmutableDictionary<string, object> plainValue)
    {
        TargetAddress = (Address)plainValue["target_address"];
    }
}

// PolymorphicAction<T> requires concrete action classes marked with
// ActionTypeAttribute.
// There is only one required parameter to ActionTypeAttribute,
// which takes a unique identifier of the action type.
// This is used for serialization and deserialization under the hood.
[ActionType("create_character")]
public sealed class CreateCharacter : ActionBase
{
    public override IAccountStateDelta Execute(IActionContext context)
    {
        var state = (ImmutableDictionary<string, uint>)
            context.PreviousStates.GetState(TargetAddress);
        if (!TargetAddress.Equals(context.Signer))
            throw new Exception(
                "TargetAddress of CreateCharacter action only can be " +
                "the same address to the Transaction<T>.Signer."
            );
        else if (!(state is null))
            throw new Exception("Character was already created.");
        return context.PreviousStates.SetState(
            TargetAddress,
            ImmutableDictionary<string, uint>.Empty.Add("hp", 20)
        );
    }
}

[ActionType("attack")]
public sealed class Attack : ActionBase
{
    public override IAccountStateDelta Execute(IActionContext context)
    {
        var state = (ImmutableDictionary<string, uint>)
            context.PreviousStates.GetState(TargetAddress);
        return context.PreviousStates.SetState(
            TargetAddress,
            state.SetItem("hp", Math.Max(state["hp"] - 5, 0))
        );
    }
}

[ActionType("heal")]
public sealed class Heal : ActionBase
{
    public override IAccountStateDelta Execute(IActionContext context)
    {
        var state = (ImmutableDictionary<string, uint>)
            context.PreviousStates.GetState(TargetAddress);
        return context.PreviousStates.SetState(
            TargetAddress,
            state.SetItem("hp", Math.Min(state["hp"] + 5, 20))
        );
    }
}

Constructors

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PolymorphicAction()

Do not use this constructor. Use PolymorphicAction(T) instead.

Declaration
[Obsolete]
public PolymorphicAction()
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PolymorphicAction(T)

Creates a new PolymorphicAction<T> instance wrapping an innerAction.

Declaration
public PolymorphicAction(T innerAction)
Parameters
Type Name Description
T innerAction

An instance of T (or one of its subtypes) to wrap.

Exceptions
Type Condition
MissingActionTypeException

Thrown when the class of the given innerAction is not annotated with ActionTypeAttribute.

Properties

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InnerAction

The wrapped action object of T (or one of its subtypes).

Declaration
public T InnerAction { get; }
Property Value
Type Description
T
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PlainValue

Serializes values bound to an action, which is held by properties (or fields) of an action, so that they can be transmitted over network or saved to persistent storage.

Serialized values are deserialized by LoadPlainValue(IImmutableDictionary<String, Object>) method later.

It uses .NET's built-in serialization mechanism.

Declaration
public IImmutableDictionary<string, object> PlainValue { get; }
Property Value
Type Description
IImmutableDictionary<String, Object>

A value which encodes this action's bound values (held by properties or fields). It has to be serializable.

See Also
LoadPlainValue(IImmutableDictionary<String, Object>)

Methods

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Execute(IActionContext)

Executes the main game logic of an action. This should be deterministic.

Through the context object, it receives information such as a transaction signer, its states immediately before the execution, and a deterministic random seed.

Other “bound” information resides in the action object in itself, as its properties (or fields).

A returned AddressStateMap object functions as a delta which shifts from previous states to next states.

Declaration
public IAccountStateDelta Execute(IActionContext context)
Parameters
Type Name Description
IActionContext context

A context object containing addresses that signed the transaction, states immediately before the execution, and a PRNG object which produces deterministic random numbers. See IActionContext for details.

Returns
Type Description
IAccountStateDelta

A map of changed states (so-called "dirty").

Remarks

This method should be deterministic: for structurally (member-wise) equal actions and IActionContexts, the same result should be returned.

For randomness, never use Random nor any other PRNGs provided by other than Libplanet. Use Random instead.

Also do not perform I/O operations such as file system access or networking. These bring an action indeterministic.

See Also
IActionContext
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LoadPlainValue(IImmutableDictionary<String, Object>)

Deserializes serialized data (i.e., data PlainValue property made), and then fills this action's properties (or fields) with the deserialized values.

Declaration
public void LoadPlainValue(IImmutableDictionary<string, object> plainValue)
Parameters
Type Name Description
IImmutableDictionary<String, Object> plainValue

Data (made by PlainValue property) to be deserialized and assigned to this action's properties (or fields).

See Also
PlainValue

Operators

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Implicit(T to PolymorphicAction<T>)

For convenience, an inner action T can be implicitly casted to PolymorphicAction<T>.

Declaration
public static implicit operator PolymorphicAction<T>(T innerAction)
Parameters
Type Name Description
T innerAction

An instance of T (or one of its subtypes) to wrap.

Returns
Type Description
PolymorphicAction<T>

A PolymorphicAction<T> wrapping the given innerAction.

Exceptions
Type Condition
MissingActionTypeException

Thrown when the class of the given innerAction is not annotated with ActionTypeAttribute.

Implements

IAction
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