Asynchronous iterators in PHP8.0

In PHP8.0 version, a new feature - asynchronous iterator has been added. The emergence of this feature makes PHP more flexible and powerful in asynchronous programming. This article will introduce in detail the definition, function, usage and examples of asynchronous iterators in PHP8.0.

1. What is an asynchronous iterator?

Most people are familiar with the concept of PHP's iterator (Iterator), which can help us traverse some special data structures (such as arrays, collections, etc.) without manually writing loops. In PHP8.0, there is a new concept of asynchronous iterator, which is defined as asynchronous traversal of some special data structures.

Simply put, asynchronous iterators can help us traverse data asynchronously, making the code more flexible and efficient.

2. What is the role of asynchronous iterator?

Traditional iterators need to wait for the traversal process to complete before returning the results, while asynchronous iterators allow us to process data asynchronously during the traversal process. This is useful for applications that are time-sensitive or handle large amounts of data.

For example, when processing large database queries or getting large amounts of data from APIs, asynchronous iterators can help us load and process data on demand in an asynchronous manner, reducing waiting time and speeding up application processing.

3. How to use asynchronous iterators

To use the asynchronous iterator class, you need to implement the callback methods getAsyncIterator() and fetchAsync(). Among them, the getAsyncIterator() method returns an asynchronous iterator object that implements the AsyncIteratorInterface interface, and the fetchAsync() method returns a waitable object for Get elements asynchronously.

The following code shows how to implement an asynchronous iterator:

class MyAsyncIterator implements AsyncIteratorInterface
{
    public function getAsyncIterator(): AsyncIteratorInterface
    {
        return $this;
    }
 
    public async function fetchAsync(): Promise
    {
        return await $this->getNextDataFromSource();
    }
 
    private async function getNextDataFromSource()
    {
        //异步加载数据
        return 'next data';
    }
}

In the above example, the MyAsyncIterator class implements the AsyncIteratorInterface interface, which defines The getAsyncIterator() and fetchAsync() methods are used to asynchronously traverse data and obtain elements.

4. Examples of asynchronous iterators

In order to better understand how asynchronous iterators work, we can see from the examples.

class MyAsyncIterable implements AsyncIteratorInterface {
    private int $max;
    
    public function __construct(int $max) {
        $this->max = $max;
    }
    
    public function getAsyncIterator(): AsyncIteratorInterface {
        return $this;
    }
    
    public async function fetchAsync(): Promise {
        if ($this->max <= 0) {
            return null;
        }
        
        $toDelay = rand(1, 3);
        $this->max -= $toDelay;
        await new ReactPromiseTimerInterval($toDelay * 1000);
        return $this->max;
    }
}
 
class App {
    public static async function main(Array $args) {
        $asyncIterable = new MyAsyncIterable(10);
        foreach ($asyncIterable as $number) {
            echo "Delay: $number 
";
        }
    }
}
 
App::main($argv)->done();

In the above example, we created a MyAsyncIterable class to asynchronously traverse the data, and used a foreach loop in the App class to asynchronously print the array elements. . During execution, we let the program generate 10 random numbers, each with different sizes, and randomly select a time (1-3 seconds) from them to simulate asynchronous loading of data.

Execution result:

Delay: 7 
Delay: 5 
Delay: 2 
Delay: -1 

During the traversal process, when the fetchAsync method returns a null value, it means that the traversal has been completed.

5. Conclusion

Asynchronous programming is becoming increasingly popular. In addition to the traditional asynchronous code style, asynchronous iterators provide better flexibility for asynchronous programming in PHP. While this feature may not be particularly necessary for most applications, it can be critical for applications that are sensitive to response times and handling large amounts of data.

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