Designing with Swift: Exploring Template Method Pattern
We all know that Swift is a powerful language for creating robust and efficient applications. It has become the go-to language for many developers due to its clean syntax and its ability to quickly develop applications. In this article, we’ll be exploring one of the design patterns in Swift, the Template Method Pattern.
The Template Method Pattern is a structural pattern that defines the skeleton of an algorithm in a method, deferring some steps to subclasses. It allows us to define the basic steps of an algorithm and allow subclasses to provide concrete implementation. This pattern is useful when you have a class that needs to perform a sequence of steps but the details of those steps may vary depending on the situation.
Let’s take a look at an example. We have a class called `FileLoader` which will be responsible for loading a file from a given path. The basic steps of this algorithm are as follows:
1. Validate the file path
2. Open the file
3. Read the contents of the file
4. Close the file
These are the four basic steps of our algorithm. We don’t want to define the implementation details of these steps in this class, so we’ll use the Template Method Pattern.
First, let’s create the FileLoader class. Here’s the code for the FileLoader class:
class FileLoader {
func loadFile(filePath: String) {
validateFilePath(filePath: filePath)
openFile(filePath: filePath)
readFileContents(filePath: filePath)
closeFile(filePath: filePath)
}
// This is the "template method"
// It defines the skeleton of the algorithm
// The details of the algorithm are deferred to subclasses
func validateFilePath(filePath: String) {
// Default implementation
}
func openFile(filePath: String) {
// Default implementation
}
func readFileContents(filePath: String) {
// Default implementation
}
func closeFile(filePath: String) {
// Default implementation
}
}
As you can see, we have defined the four steps of our algorithm in the `loadFile` method. We have also defined four empty methods for each step of the algorithm. These methods will be overridden by subclasses.
Now, let’s create a subclass of the FileLoader class. We’ll call it `JSONFileLoader`. This class will be responsible for loading a JSON file. Here’s the code for the JSONFileLoader class:
class JSONFileLoader: FileLoader {
override func validateFilePath(filePath: String) {
// Validate the file path
}
override func openFile(filePath: String) {
// Open the file
}
override func readFileContents(filePath: String) {
// Read the contents of the file
}
override func closeFile(filePath: String) {
// Close the file
}
}
As you can see, we have overridden the four methods of the FileLoader class. We can now provide concrete implementations for each of the steps in our algorithm.
So, the Template Method Pattern allows us to define the basic steps of an algorithm and allows subclasses to provide concrete implementations. This pattern is useful when you have a class that needs to perform a sequence of steps but the details of those steps may vary depending on the situation.
In this article, we explored the Template Method Pattern in Swift. We saw how the pattern allows us to define the basic steps of an algorithm and allows subclasses to provide concrete implementations. We then implemented the pattern using a simple example of a file loader class. I hope this article was helpful in understanding the Template Method Pattern in Swift.