proxy top-level constant Null safety

Object const proxy

This annotation is deprecated and will be removed in Dart 2.

Dart 2 has a more restrictive type system than Dart 1, and it requires method access to be either through a known interface or by using dynamic invocations. The original intent of @proxy (to implement a class that isn't known statically, as documented at the end of this text), is not supported by Dart 2. To continue to perform dynamic invocations on an object, it should be accessed through a reference of type dynamic.

The annotation @proxy marks a class as implementing members dynamically through noSuchMethod.

The annotation applies to any class. It is inherited by subclasses from both superclass and interfaces.

If a class is annotated with @proxy, or it implements any class that is annotated, then all member accesses are allowed on an object of that type. As such, it is not a static type warning to access any member of the object which is not implemented by the class, or to call a method with a different number of parameters than it is declared with.

The annotation does not change which classes the annotated class implements, and does not prevent static warnings for assigning an object to a variable with a static type not implemented by the object.

The suppression of warnings only affect static type warnings about member access. The runtime type of the object is unaffected. It is not considered to implement any special interfaces, so assigning it to a typed variable may fail in checked mode, and testing it with the is operator will only return true for types it actually implements or extends. Accessing a member which isn't implemented by the class will cause the noSuchMethod method to be called normally, the @proxy annotation merely states the intent to handle (some of) those noSuchMethod calls gracefully.

A class that marked as @proxy should override the noSuchMethod declared on Object.

The intent of the @proxy notation is to create objects that implement a type (or multiple types) that are not known at compile time. If the types are known at compile time, a class can be written that implements these types.


const Object proxy = _Proxy()