How do I create a selector that takes an argument?

[didusmell]

As the title says, how do I create a selector that takes an argument? just like this in ReselectJS

[brianegan]

You have a few options. First, you can write a fuction that creates a selector. Building on the example in the readme, let's say you wanted to make the affordable products selector configurable:

Selector<AppState, List<Product>> createAffordableProductsSelector(double price) {
  return createSelector1(
    productsSelector,
      (products) => products.where((product) => product.price < price),
    );
}

// Usage
final affordableProductsSelector = createAffordableProductsSelector(10.00);
final affordableProducts = affordableProductsSelector(appState);

The other option: Although a selector only takes in 1 parameter, that parameter can be anything you want. It can be a class that holds multiple values, or a Dart 3 record.

typedef Params = (AppState state, double price);

final affordableProductsSelector = createSelector1<Params, (List<Product>, double), List<Product>>(
    (params) => (productsSelector(params.$2), params.$2),
    (result) => result.$1.where((product) => product.price < result.$2),
);

[jamesncl]

Great answer, I think it would be helpful to add this to the README - see my pull request. I amended the second example - I'm pretty sure it should be productsSelector(params.$1) instead of productsSelector(params.$2)