Function PatternSwitcher 

pub fn PatternSwitcher<State, P, V>(
    key: impl Into<ChildKey>,
    pattern: P,
    child: V,
) -> PatternSwitcherView<State, P>
where
    State: 'static,
    P: TransitionPattern + Clone + 'static,
    V: View<State>,

PascalCase alias for pattern_switcher (mirrors the AnimatedOpacity/ animated_opacity dual naming).