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This article shares with you some introduction to the Abstract Syntax Tree (AST) in the new features of PHP7. The content is very good. Friends in need can refer to it. I hope it can help everyone.
This article analyzes the changes brought about by the new feature of PHP7, Abstract Syntax Tree (AST). Share it with everyone for your reference, as follows:
Most of the content here is based on the RFC document of AST: https://wiki.php.net/rfc/abstractsyntaxtree, which is excerpted from the source document for ease of understanding. section is introduced.
This article will not tell you what an abstract syntax tree is. This needs to be understood by yourself. This article only describes some changes that AST brings to PHP.
An important change in the core of PHP7 is the addition of AST. In PHP5, the execution process from php scripts to opcodes is:
Lexing: lexical scanning analysis, converting source files into token streams;
Parsing: Syntax analysis, op arrays are generated at this stage.
In PHP7, op arrays are no longer directly generated during the syntax analysis phase, but AST is generated first, so there is one more step in the process:
Lexing : Lexical scan analysis, convert the source file into a token stream;
Parsing: Syntax analysis, generate an abstract syntax tree from the token stream;
Compilation: Generate op arrays from abstract syntax trees.
From the above steps, this is one more step than the previous process, so according to common sense, this will increase the program execution time and memory usage. But in fact, the memory usage has indeed increased, but the execution time has decreased.
The following results are obtained by testing three scripts: small (about 100 lines of code), medium (about 700 lines), and large (about 2800 lines). Test script: https://gist.github .com/nikic/289b0c7538b46c2220bc.
Execution time of compiling each file 100 times (note that the test results of the article are from 14 years, when PHP7 was still called PHP-NG):
php-ng | php-ast | diff | |
SMALL | 0.180s | 0.160s | -12.5% |
MEDIUM | 1.492s | 1.268s | -17.7% |
LARGE | 6.703s | 5.736s | -16.9% |
Memory peak in a single compilation:
php-ng | php-ast | diff | |
SMALL | 378kB | 414kB | 9.5 % |
507kB | 643kB | 26.8% | |
1084kB | 1857kB | 71.3% |
##php-ng | php-astdiff | TIME | ||||||||||||||||
22.8ms | -11.8% | MEMORY | ||||||||||||||||
2482kB | 5.1% |
PHP5 | PHP7 | |
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$foo->{$bar['baz']}( ) | ($foo->$bar)['baz']() | ##Foo::$bar['baz']() |
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