Expando<T extends Object> final

final class Expando<T extends Object>

An Expando allows adding new properties to objects.

Does not work on numbers, strings, booleans, records, null, dart:ffi pointers, dart:ffi structs, or dart:ffi unions.

An Expando does not hold on to the added property value after an object becomes inaccessible.

Since you can always create a new number that is identical to an existing number, it means that an expando property on a number could never be released. To avoid this, expando properties cannot be added to numbers. The same argument applies to strings, booleans and null, which also have literals that evaluate to identical values when they occur more than once. In addition, expando properties can not be added to records because records do not have a well-defined persistent identity.

There is no restriction on other classes, even for compile time constant objects. Be careful if adding expando properties to compile time constants, since they will stay alive forever.

Constructors

Expando()

Expando([String? name])

Creates a new Expando. The optional name is only used for debugging purposes and creating two different Expandos with the same name yields two Expandos that work on different properties of the objects they are used on.

Implementation

external Expando([String? name]);

Properties

hashCode no setter inherited

int get hashCode

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.

Inherited from Object.

Implementation

external int get hashCode;

name final

final String? name

The name of the this Expando as passed to the constructor.

If no name was passed to the constructor, the value is the null value.

Implementation

final String? name;

runtimeType no setter inherited

Type get runtimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation

external Type get runtimeType;

Methods

noSuchMethod() inherited

dynamic noSuchMethod(Invocation invocation)

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.

Implementation

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

toString() override

String toString()

Expando toString method override.

Implementation

String toString() => "Expando:$name";

Operators

operator ==() inherited

bool operator ==(Object other)

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.

Inherited from Object.

Implementation

external bool operator ==(Object other);

operator

T? operator [](Object object)

Gets the value of this Expando's property on the given object.

If the object hasn't been expanded, the result is the null value.

The object must not be a number, a string, a boolean, a record, null, a dart:ffi pointer, a dart:ffi struct, or a dart:ffi union.

Implementation

external T? operator [](Object object);

operator []=()

void operator []=(Object object, T? value)

Sets this Expando's property value on the given object to value.

Properties can effectively be removed again by setting their value to null.

The object must not be a number, a string, a boolean, a record, null, a dart:ffi pointer, a dart:ffi struct, or a dart:ffi union.

Implementation

external void operator []=(Object object, T? value);