checked top-level constant

const checked = const _Checked()

Used to annotate a parameter of an instance method that overrides another method.

Indicates that this parameter may have a tighter type than the parameter on its superclass. The actual argument will be checked at runtime to ensure it is a subtype of the overridden parameter type.

DEPRECATED: Use the covariant modifier instead.

Implementation 

const _Checked checked = const _Checked()