How to implement the bottom layer of php array

PHP is a server-side scripting language that is widely used to develop web applications. Array is one of the most commonly used data structures in PHP language, which can store multiple values ​​and access these values ​​by index or association. In PHP, the underlying implementation of the array is one of the keys, because it directly affects the performance and reliability of the program.

PHP's array implementation is different from other programming languages. It is a hash table, also called a hash table. This data structure uses memory and disk space to store and access elements. The PHP hash table includes a bucket array and a data array. The bucket array maintains the data storage location corresponding to the hash value, and the data array contains the actual stored value.

When creating a new PHP array, both the bucket array and the data array are empty. When adding an element to the array, PHP will calculate the hash value of the element and store the hash value in the linked list at the corresponding position in the bucket array. If there is no element at this position, then the linked list has only one element, that element. If an element already exists at the position, the new element will be added to the linked list at that position.

When you get an element from a PHP array, PHP calculates its hash value and matches the hash value to the position in the bucket array. If there is an element containing the hash value at a certain position, PHP will traverse the linked list, find the element containing the key, and return the value of the element. If the element is not found, PHP will return a null value.

It automatically resizes the bucket array when the array becomes too large or too sparse. This process involves some complex algorithms to ensure good performance on different data sets. One advantage of a hash table is that it can perform insertion, deletion, and lookup operations with constant time complexity. This means that for large data sets, the performance of PHP hash tables will not be affected too much.

However, hash tables may conflict under certain circumstances. In this case, if two keys have the same hash value, they will be stored in the same location in the linked list. When accessing these keys, PHP will traverse the entire linked list to find the appropriate key, which will cause performance degradation. To avoid this, PHP implements a technique called "open chaining", which stores keys with the same hash value on a separate bucket instead of on the same linked list.

In general, the hash table implemented at the bottom of PHP array is an efficient data structure, which greatly simplifies the operation of arrays. However, it also requires attention to the problem of hash collisions, so programmers need to understand how hash tables work and take appropriate precautions to avoid these problems. In practical applications, understanding the working principles and characteristics of the underlying implementation of PHP arrays will help programmers write more efficient and reliable programs.

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