typedStreamTransformer<S, T> function

StreamTransformer<S, T> typedStreamTransformer <S, T>(StreamTransformer transformer)

Creates a wrapper that coerces the type of transformer.

This soundly converts a StreamTransformer to a StreamTransformer<S, T>, regardless of its original generic type, by asserting that the events emitted by the transformed stream are instances of T whenever they're provided. If they're not, the stream throws a CastError.

Implementation 

StreamTransformer<S, T> typedStreamTransformer<S, T>(
        StreamTransformer transformer) =>
    transformer is StreamTransformer<S, T>
        ? transformer
        : new _TypeSafeStreamTransformer(transformer);