PHP array implementation principle efficiency

PHP is a popular server-side programming language that is widely used to develop web applications. In PHP, an array is a common data structure that can store multiple values, indexed by unique key-value pairs. This article will introduce the implementation principles and performance of PHP arrays.

The implementation principle of PHP array

The implementation of PHP array is slightly different from that of most programming languages. In PHP, an array is actually a class, rather than the traditional array implementation used in C. This means that PHP arrays can not only store simple data types such as integers and strings like traditional arrays, but also complex objects.

The internal implementation principle of PHP array is based on hash table. A hash table is a key-value pair storage structure that uses a hash function to map a key to a position in an array. In PHP, hash tables are dynamically resized, when elements need to be added, it reallocates memory to accommodate the new elements and shrinks the memory when needed to save space.

As mentioned above, PHP arrays are implemented using hash tables. The main advantage of using a hash table is the ability to find elements quickly. By using hash functions we can locate elements in an array in constant time and access them with O(1) time complexity.

Hash functions in PHP are string based, if we want to store different types of values ​​in the same array, they need to be converted to strings for hashing. This process is called casting. For example, in the following code:

$array = array(1, “2”, $obj, 4.0);

If $obj is an object, then it will be converted to the string "Object". The string representation of integers and floats does not change, so we can use the value to compare elements and hash.

Efficiency of PHP arrays

Because PHP arrays use hash tables, operations on data structures have faster execution times. Here are the time complexities and descriptions of some common operations:

1. Accessing elements: O(1) - just need to calculate the hash and access the elements in the array
2. Add elements: O(1) - Usually just need to insert new element at appropriate index position
3. Remove element: O(1) - Just need to calculate hash value and delete element in array
4. Iterate over element :O(n) - Need to loop through the entire array to get all elements

As you can see, PHP arrays are very efficient for most operations. However, PHP's performance can be limited when it comes to large arrays. This is because PHP arrays are dynamic, so when elements are added or removed, it needs to reallocate memory to maintain the size of the array. This process can be slow, especially in arrays with large amounts of data.

Also, not all hash functions are perfect. The performance of PHP arrays may suffer if the hash function creates collisions in certain data sets. In PHP 7.3, the hashing algorithm has been updated to reduce hash collisions similar to Jenkins' algorithm.

Conclusion

PHP array is a very powerful data structure suitable for storing large amounts of data and retrieving it quickly. Its implementation is based on a hash table, allowing access to elements in an array in constant time. While PHP arrays are performant in most cases, they can suffer from dynamic memory allocation when working with large data sets, so their implementation needs to be carefully considered.

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