Detail the underlying implementation of php7 arrays

With the release of PHP7, its performance has been significantly improved. Among them, the underlying implementation of arrays has been significantly improved and has become one of the most significant improvements in PHP7. In this article, we will explore the underlying implementation of arrays in PHP7 and how to make it more efficient.

Before PHP7, arrays were one of the core features of PHP, and their underlying implementation used a data structure called a "hash table". In short, a hash table is a data structure that indexes data according to its keys, and these indexes can greatly speed up access to data. Hash tables in PHP were first introduced in PHP4 and are still used today.

However, PHP’s hash table implementation is not sufficient to handle large-scale data processing. In PHP5, to solve this problem, a hash table implementation called "detached linked list" was introduced. This implementation handles hash collisions better, but can still suffer from performance issues in some cases.

In PHP7, the hash table implementation has been fully optimized. Now, PHP's hash tables are grouped according to buckets, and each bucket contains a linked list. When a new element is inserted, PHP7's hash table inserts it into the bucket's linked list, and the array size is adjusted during the insertion process. Specifically, PHP7's hash table can automatically grow or shrink the size of its internal array to accommodate the actual size of the data.

In addition, PHP7's hash table also adds a variant called "dense hash table", which can better handle consecutive integer keys (such as 0, 1, 2 ...). A dense hash table is a special hash table that maps keys directly to indexes in an array, thus avoiding the problem of hash collisions. The performance advantages of dense hash tables are particularly prominent when dealing with integer indexes.

Another important change in PHP7 is that it introduces a method called "bitmap optimization". Bitmap is a binary data structure that is often used to process large amounts of Boolean data. In PHP7, bitmaps are used to optimize the internal implementation of arrays. Specifically, it can avoid some unnecessary memory allocations, thereby making the array's memory usage more efficient.

In general, PHP7’s array implementation is quite excellent. It uses some modern data structures and algorithms while maintaining the flexibility and ease of use of PHP. In PHP7, the performance and memory usage of arrays have been significantly improved, making PHP more suitable for application scenarios oriented to large-scale data processing.

When using PHP7, we should take advantage of these new features as much as possible. For example, when processing large-scale data sets, dense hash tables can be used to achieve higher performance. In addition, in order to maximize the performance advantages of arrays, we can also try to use more efficient algorithms and data structures, such as the newly introduced Generator and Closure in PHP7.

In general, the array implementation of PHP7 is an important direction for PHP language performance optimization. By deeply understanding its underlying implementation and using the latest features and technologies, we can process large-scale data sets in PHP applications more efficiently.

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