createSelector1

Selector<S, R> createSelector1<S, T1, R>(

  1. Selector<S, T1> selector1,

  2. R combiner(
    1. T1
    )
)

Creates a memoized selector that caches its result.

The selector will only recompute when the input changes. This is useful for expensive computations derived from state.

Example:

final getTodos = (AppState state) => state.todos;
final getFilter = (AppState state) => state.filter;

final getVisibleTodos = createSelector1(
getTodos,
(todos) => todos.where((t) => !t.completed).toList(),
);

Implementation

Selector<S, R> createSelector1<S, T1, R>(
  Selector<S, T1> selector1,
  R Function(T1) combiner,
) {
  T1? lastInput;
  R? lastResult;
  var hasCache = false;

return (S state) {
final input = selector1(state);


if (hasCache && identical(input, lastInput)) {
return lastResult as R;
}


lastInput = input;
lastResult = combiner(input);
hasCache = true;


return lastResult as R;
};
}