Swift downcast plus#

The unary plus operator (+) simply returns the value it operates on, without any change. Let invertedBits = ~initialBits // equals 11110000

The bitwise NOT operator (~) inverts all bits in a number.

The logical NOT operator (!) inverts a Boolean value so that true becomes false, and false becomes true. The tables below list the operators declared in Swift. Like, the assignment operator ( =) doesnвЂ™t return a value, to prevent it from being mistakenly used when the equal to operator ( =) is intended. Swift supports most standard C operators and improves several capabilities to eliminate common coding errors. For example, the addition operator ( +) adds two numbers, as in let i = 1 + 2.

It is possible to use generic function syntax to perform an upcast and additional checks on your type before entering the body.An operator is a special symbol or phrase that you use to check, change, or combine values.

Outside a loop, you can perform optional downcasting with as? or forced downcasting with as! Forced downcasting should be actively avoided and only used when you know with certainty that it will succeed.

Downcasting in a loop can be done with for case let _ as _.

Downcasting to a protocol type or an struct/class type can have very different results in terms of accessible methods and properties.

Upcasting can be done explicitly with the as operator, although such an operation isnвЂ™t even required when passing a type into a collection or function/method as Swift is able to implicitly upcast when you declare the desired type.

Wrap UpДЄnd thatвЂ™s it! Hopefully this article has shown that working with polymorphism isnвЂ™t nearly as difficult as it sounds. Sure enough, we now have access to its two protocol methods and single instance method. In this example above, we are optionally downcasting our input argument to our StructLevelTwo type. Notice also that instead of only accessing protocol methods, we can now access our levelTwo instance method. Whereas two instances performed method calls in the previous example, this time we only have one instance of type StructLevelTwo. While StructLevelTwo adopts ProtocolLevelTwo, we can clearly see that the results of a class/struct downcast are very different. Downcast to a struct/class type (lines 17вЂ“31) In our example, we have two instances that conform to this protocol: levelTwo which adopts it directly, and levelThree which adopts it through protocol inheritance. As you have probably guessed this means that we can only access our protocol methods from level one and two. In this case we are downcasting to our ProtocolLevelTwo type. Downcast to protocol type (lines 13вЂ“16)ДЇor case let is a useful structure when we want to downcast an element and bind it to a constant within a loop, and the next two examples use it to good effect. It is important to emphasize that is only performs a check not a downcast, so we can still only access the same protocolMethodOne that we had available in the previous example. You may remember that we have two instances that do this, levelTwo and levelThree, which is why we have the print out reveals the method being called twice. In this case, notice that we are checking if the instance conforms to ProtocolLevelTwo. We can use the is keyword to check that an instance is a certain type. However, if we want only some of the objects to perform a task, or if we want to access an interface that is further down our hierarchy, we need to do a little more work. Performing Type Checks and DowncastingДЄs we saw in the previous example, its very easy to work with the instances in our collection by accessing their shared interface. Now all three of our elements are able to access the method available in ProtocolLevelOne and no others. Notice in the example, that no explicit upcasting is used in the append methods.

Swift downcast