Downcast subtype operator

[NN---]

The cast operator using () or “as” allows writing any target type.
It would be nicer to have a restriction only for subtypes.
It is possible to write such extension method now but only a specific type.
Generics do not support high order types to write a single method for any type.

Before:

MyType m:

(String)m // compiles , always fail in runtime
(MySubType) // compiles

workaround:

class MyTypeExt{
 public static T Cast<T>(this MyType m) where T:MyType => (T)m;
}

// repeat for any type needed

With subtype operator: (syntax just an example)

m subtype_cast string // doesn’t compile
m subtype_cast MySubType // compiles

[KennethHoff]

By default both x as X and (X)x gives you a warning if it's not a hierarchy. Make those warnings into errors and you're good - no changes required.

[HaloFour]

The cast operator using () or “as” allows writing any target type.

Are you sure? If I try to cast from MyType to string I already get error CS0030 or CS0039. I have to upcast to object first before it will let me downcast to string.