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