dot_cast 1.2.0

This package provides the user with extension methods for casting objects allowing you to write less and cleaner code.

This package allows you to cast and check your Objects in a more convenient way.

Features

This package contains functions and extensions for casting and checking objects.

Functions

The functions are just another way of casting and checking objects which might make it a bit more readable and usable.

cast

With cast you can force a cast. It will throw an error if the cast fails.

Car car = cast<Car>(vehicle); // vehicle as Car

tryCast

If you are not sure if the cast will be valid, you can use tryCast to receive a null when the cast fails.

Car? car = tryCast<Car>(vehicle); // vehicle is Car ? vehicle as Car : null

isType

You can use isType to check wether an Object is of a certain type. It will return true if the Object is the same type or a subclass.

bool isCar = isType<Car>(vehicle); // vehicle is Car

isExactType

You can also use isExactType to check wether an Object is of a certain type. Unlike isType, this will only return true if the Object is exactly the given type.

bool isCar = isExactType<Car>(vehicle); // vehicle.runtimeType == Car

Extensions

There also are extensions that allow for a more easy way to cast and check objects and continue using them in your code.

With .cast you can force a cast. You should only do this if you are 100% certain that the cast is valid, or else an error is thrown.

Car car = vehicle.cast<Car>(); // vehicle as Car

If you are not 100% sure .cast is going to work, you can use .tryCast. .tryCast will return null if the cast fails.

Car? car = vehicle.tryCast<Car>(); // vehicle is Car ? vehicle as Car : null

These two extensions make it easier to use your casted objects.

For example when you only need to show items when your state has been loaded, you simply do the following:

final items = state.tryCast<Loaded>()?.items;

Also, both isType and isExactType have equivalent extensions available.

bool isCar = vehicle.isType<Car>(); // vehicle is Car

bool isVehicle = car.isExactType<Vehicle>(); // car.runtimeType == Vehicle

Real World Examples

Below you will find real world examples for the use of this package.

BlocSelector

I've used the flutter_bloc package for a long time. One of my favorite widgets from that package is the BlocSelector.

The BlocSelector allows you to rebuild a piece of your UI on a very specific state change. Let's say we want to show the total amount of our shopping basket.

We can only show the amount when the basket has been loaded and there are products available, else we just show 0. Without dot_cast, we could write it like this:

BlocSelector<BasketBloc, BasketState, double>(
    selector: (state) {
        if (state is! BasketLoaded) {
            return 0.0; // if it has not been loaded, return default
        }
        final products = state.product; // We can now get the products
        if (products == null) { 
            return 0.0; // if products is null, return default
        }
        // Here products has been promoted to be a non-nullable object
        return products.totalPrice; 
    },
    builder: (context, state) {
        // Build the widget
    }
)

Or as a single expression:

BlocSelector<BasketBloc, BasketState, double>(
    selector: (state) => state is BasketLoaded ? state.products?.totalPrice ?? 0.0 : 0.0,
    builder: (context, state) {
        // Build the widget
    }
)

I personally think combining all the different syntaxes makes the code look kind of messy. We have a test operator (is), the conditional operator (test ? true : false), null-check (?) and the if-null operator (??), all in one line.

With dot_cast, we can turn remove half of those. The result looks like this:

BlocSelector<BasketBloc, BasketState, double>(
    selector: (state) => state.tryCast<BasketLoaded>()?.products?.totalPrice ?? 0.0,
    builder: (context, state) {
        // Build the widget
    }
)

In this last example we are able to write a single, readable, line. Hopefully this gives you an idea on how this package can help you.

Other state management packages like flutter_redux and my own etos_flutter use the same concepts to allow for specific rebuilds.