InstanceHandle#

Represents a reference handle to an instance and encodes the lookup key information for the persistent key-value store.

This class serves as a lightweight identifier for entity instances, containing both the instance identifier and type identifier for efficient storage and retrieval operations.

Constructors#

InstanceHandle() const#

Creates an InstanceHandle with the specified instance and type identifiers.

instanceId: The instance identifier (defaults to 0). typeId: The type identifier hash (defaults to 0).

const InstanceHandle([this.instanceId = 0, this.typeId = 0]);

InstanceHandle.fromJson() factory#

Creates an InstanceHandle from a JSON-serializable map.

values: A map containing instance data with keys kInstanceIdKey and kInstanceTypeKey. The type key can be either an integer or a string that will be converted to a type hash using toTypeId.

factory InstanceHandle.fromJson(Map values) {
  int id = values[kInstanceIdKey] ?? 0;
  int typeId = 0;
  final any = values[kInstanceTypeKey] ?? values['type'];
  if (any is int) {
    typeId = any;
  } else if (any is String) {
    typeId = toTypeId(any);
  }
  return InstanceHandle(id, typeId);
}

InstanceHandle.fromJsonArray() factory#

Creates an InstanceHandle from a JSON array.

array: A two-element array where the first element is the instance ID and the second element is the type ID. Returns a null handle if the array does not contain exactly two elements.

factory InstanceHandle.fromJsonArray(List<dynamic> array) {
  if (array.length != 2) {
    return InstanceHandle();
  }
  final instanceId = (array[0] is int) ? array[0] : 0;
  final typeId = (array[1] is int) ? array[1] : 0;
  return InstanceHandle(instanceId, typeId);
}

InstanceHandle.nullHandle() factory#

Creates a null InstanceHandle with both instanceId and typeId set to 0.

factory InstanceHandle.nullHandle() {
  return InstanceHandle();
}

Properties#

hashCode no setter override#

The hash code for this object.

A hash code is a single integer which represents the state of the object that affects operator == comparisons.

All objects have hash codes. The default hash code implemented by Object represents only the identity of the object, the same way as the default operator == implementation only considers objects equal if they are identical (see identityHashCode).

If operator == is overridden to use the object state instead, the hash code must also be changed to represent that state, otherwise the object cannot be used in hash based data structures like the default Set and Map implementations.

Hash codes must be the same for objects that are equal to each other according to operator ==. The hash code of an object should only change if the object changes in a way that affects equality. There are no further requirements for the hash codes. They need not be consistent between executions of the same program and there are no distribution guarantees.

Objects that are not equal are allowed to have the same hash code. It is even technically allowed that all instances have the same hash code, but if clashes happen too often, it may reduce the efficiency of hash-based data structures like HashSet or HashMap.

If a subclass overrides hashCode, it should override the operator == operator as well to maintain consistency.

@override
int get hashCode => Object.hash(instanceId, typeId);

instanceId final#

The unique identifier of the instance.

final int instanceId;

isNull no setter override#

Indicates whether the object represents a null value.

Returns true if the object is considered null according to its implementation, false otherwise.

@override
bool get isNull => typeId == 0;

runtimeType no setter inherited#

A representation of the runtime type of the object.

Inherited from Object.

external Type get runtimeType;

typeId final#

The type identifier of the instance, hash of the type name.

final int typeId;

Methods#

noSuchMethod() inherited#

Invoked when a nonexistent method or property is accessed.

A dynamic member invocation can attempt to call a member which doesn't exist on the receiving object. Example:

dynamic object = 1;
object.add(42); // Statically allowed, run-time error

This invalid code will invoke the noSuchMethod method of the integer 1 with an Invocation representing the .add(42) call and arguments (which then throws).

Classes can override noSuchMethod to provide custom behavior for such invalid dynamic invocations.

A class with a non-default noSuchMethod invocation can also omit implementations for members of its interface. Example:

class MockList<T> implements List<T> {
  noSuchMethod(Invocation invocation) {
    log(invocation);
    super.noSuchMethod(invocation); // Will throw.
  }
}
void main() {
  MockList().add(42);
}

This code has no compile-time warnings or errors even though the MockList class has no concrete implementation of any of the List interface methods. Calls to List methods are forwarded to noSuchMethod, so this code will log an invocation similar to Invocation.method(#add, [42]) and then throw.

If a value is returned from noSuchMethod, it becomes the result of the original invocation. If the value is not of a type that can be returned by the original invocation, a type error occurs at the invocation.

The default behavior is to throw a NoSuchMethodError.

Inherited from Object.

@pragma("vm:entry-point")
@pragma("wasm:entry-point")
external dynamic noSuchMethod(Invocation invocation);

toJson()#

Converts this instance handle to a JSON-serializable map.

Returns a map containing:

• kInstanceIdKey: The instance identifier
• kInstanceTypeKey: The type identifier

Map<String, dynamic> toJson() => <String, dynamic>{
      kInstanceIdKey: instanceId,
      kInstanceTypeKey: typeId,
    };

toJsonArray()#

Converts this instance handle to a JSON-serializable array.

Returns a two-element array: [instanceId, typeId].

List<int> toJsonArray() {
  return [instanceId, typeId];
}

toString() inherited#

A string representation of this object.

Some classes have a default textual representation, often paired with a static parse function (like int.parse). These classes will provide the textual representation as their string representation.

Other classes have no meaningful textual representation that a program will care about. Such classes will typically override toString to provide useful information when inspecting the object, mainly for debugging or logging.

Inherited from Object.

external String toString();

Operators#

operator ==() override#

The equality operator.

The default behavior for all Objects is to return true if and only if this object and other are the same object.

Override this method to specify a different equality relation on a class. The overriding method must still be an equivalence relation. That is, it must be:

• Total: It must return a boolean for all arguments. It should never throw.

• Reflexive: For all objects o, o == o must be true.

• Symmetric: For all objects o1 and o2, o1 == o2 and o2 == o1 must either both be true, or both be false.

• Transitive: For all objects o1, o2, and o3, if o1 == o2 and o2 == o3 are true, then o1 == o3 must be true.

The method should also be consistent over time, so whether two objects are equal should only change if at least one of the objects was modified.

If a subclass overrides the equality operator, it should override the hashCode method as well to maintain consistency.

@override
bool operator ==(Object other) {
  if (identical(this, other)) return true;
  return other is InstanceHandle &&
      other.instanceId == instanceId &&
      other.typeId == typeId;
}