PHP7 array implementation principle

PHP7 is an important version of the PHP programming language, and its array implementation principle has also changed. In this article, we will delve into the principles of PHP7 array implementation.

Array is an important data structure that can save a set of ordered data. In PHP, arrays can contain any type of value, including strings, integers, floating point numbers, etc. Arrays are very commonly used in PHP, so many adjustments and optimizations have been made to the array implementation in PHP7.

There are two data structures for implementing arrays in PHP7, namely hash tables and ordered sets. A hash table is a key-value pair storage structure that is characterized by fast data lookup. An ordered set is a collection of data arranged in index order, which is characterized by fast access to data.

In PHP7, when there are less than 6 elements stored in the array, the data structure of an ordered set is used. When there are more than 6 elements stored in the array, the hash table data structure is used.

The implementation of ordered sets is to use continuous memory space to store array elements. Since the positions of the elements are consecutive, only one memory read operation is required when accessing the array elements. This way, sorted collections provide fast access to array elements. However, when elements need to be inserted or deleted, higher time complexity will occur due to the need to move elements in the array.

The implementation of a hash table is to store elements in a hash table, and the index of the hash table is obtained by hashing the key value of the element into an integer. Since the index of the hash table is calculated through the hash function, different key values ​​​​are mapped to different index positions. In this way, elements in the array can be searched quickly. When elements are inserted or deleted, since the positions of the elements in the hash table are not consecutive, the hash table needs to be rehashed and rearranged to ensure the efficiency of the hash table.

In the implementation of arrays in PHP7, the size of the hash table is also optimized. In PHP7, the size of the hash table is a power of 2. In this way, the size of the hash table is always divisible by 2, thereby reducing the number of hash collisions.

For the array implementation of PHP7, we need to understand the following important concepts:

1. Hash function
   The hash function is to pass data of any size through a hash algorithm A function that compresses data into a fixed size. In PHP7, the key values ​​of array elements need to be calculated by a hash function before they can be stored in the hash table.
2. Hash conflict
   Hash conflict means that the key values ​​of two or more elements are calculated by the hash function and the hash values ​​obtained are the same. Hash collisions will affect the performance of hash tables, so some methods are needed to resolve hash collisions.
3. Hash function
   The hash function is a function that calculates the position of an element in a hash table. Its input is the key value, and the output is the index position in the hash table. The design of the hash function needs to consider the situation of hash collision.
4. Conflict resolution
   Conflict resolution is a method to resolve hash conflicts. Commonly used methods include zipper method, linear detection method, secondary detection method, etc. In PHP7, a chained hash table is used to resolve hash conflicts.

To sum up, PHP7’s array implementation uses two data structures: hash table and ordered set. When there are less than 6 elements stored in the array, an ordered set is used. When more than 6 elements are stored in the array, a hash table is used. The hash table is implemented through a hash table, in which the key value needs to be calculated by a hash function before it can be stored in the hash table. At the same time, PHP7 has also made a lot of optimizations, such as the hash table size being based on the power of 2, etc., thus ensuring the efficiency of the array.

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