It's the difference between these two: - JIT "Just in time" , where only the code that is needed is compiled when it's needed note, however, that after the interpreter quits, the compiled code is lot - AOT "Ahead of time" , where the all the code is compiled before it is run.
Compiling it to bytecode, which is then again interpreted by Zend, is somewhere in the middle in terms of compilation cost and runtime performance. Lol, this is a rather old thread, just realized it. Show 3 more comments. Among its tasks: Ignore comments Resolve variables, function names, and so forth and create the symbol table Construct the abstract syntax tree of your program Write the bytecode Depending on your PHP setup, this step is typically done just once, the first time the script is called.
Barry Brown Barry Brown Variable binding happens at runtime, not compile time. PHP doesn't even attempt to resolve which names are in scope at compile time?
Andrew P. Gaurang Deshpande Gaurang Deshpande 5 5 silver badges 12 12 bronze badges. A fully compiled and executable code will be in binary format.. This is one of the best explanations of the matter that I've ever encountered.
Dany Caissy 3, 13 13 silver badges 21 21 bronze badges. Max Max 2, 4 4 gold badges 31 31 silver badges 48 48 bronze badges. It can be compiled to bytecode by third party-tools, though. Using the old definitions of compiled vs. Claudiu Creanga Claudiu Creanga 6, 10 10 gold badges 55 55 silver badges 99 99 bronze badges. Doesn't Java use ahead of time compilation in most cases, though?
I'm a fairly new Java developer and we usually compile our code way before runtime. Tokenizing a source code is not compiling. Even VBScript can be regarded as a compiled language with your definition. I'm with jrockway on this, although it doesn't really answer the OP's question. It's tempting to create a taxonomy of languages in which every language is placed cleanly into each category.
But the reality isn't so neat. Almost every language is a blend of characteristics. Plus, when you get right down to it, even native machine code is "interpreted" by the processor. Your high level assertion is correct, this is a meaningless question.
Your argument however isn't very helpful, all you've done is taken fuzzy definitions and taken them to extremes. Compilation is the transformation of source into object code. I fully agree with Sedat. You can share your knowledge without being a dick to the asker — Alexandre Bourlier. At least it doesn't compile or should I say optimize the code as much as one might want it.
This code It could have detected that it is a calculation that only needs to be done the first time. Magnus Andersson Magnus Andersson 1 1 silver badge 2 2 bronze badges.
Now we have a option called generators. Dip Dip 4 4 silver badges 7 7 bronze badges. The Overflow Blog. Does ES6 make JavaScript frameworks obsolete?
Furthermore, it provides very quick feedback during development. If you have an error somewhere in your file, PHP will refuse to compile the page until you have fixed the problem, and you are able to step through execution of your code line by line until you find the problem. One major advantage to having interpreted code is that all memory used by the script is managed by PHP, and the language automatically cleans up after every script has finished.
This means that you do not need to worry about closing database links, freeing memory assigned to images, and so on, because PHP will do it for you. That is not to say you should be lazy and make PHP do all the work - good programmers clean up themselves, and let PHP work as backup in case something is missed. Get over pages of hands-on PHP learning today! The compilation process is carried out by recursively traversing the AST, as part of which some optimisations are made as well.
Most often, simple arithmetic calculations are performed, or the expressions such as strlen "test" are replaced with a direct int 4 value. As with the previous phases, there are also tools for previewing the generated OPCode. Below is an example dump provided by the VLD from a compiled Greeting class providing a sayhello method:.
By viewing the dump above, a skilled PHP developer can understand its structure on a basic level. Defined here is the class and method, followed by:. Describing the entire issue of OPCode and its components exhaustively would definitely go beyond the scope of this article. If you want to learn more about it, the official documentation will help you get started. This is the last phase of the interpretation process.
The end result is what a given script was supposed to generate, i. From the point of view of web applications, it is usually a ready source code for a website. Most of us do not think about how the PHP code is actually analysed and run on a server — especially when we entrust server and application monitoring to external service providers. Nevertheless, it is good to understand what really happens to the code of your application when it is transferred to an interpreter.
Such knowledge can help with both the security and performance analysis of a project developed in PHP. Mariusz Andrzejewski. To put it simply, the whole processing of a PHP script is carried out by the interpreter in four stages: lexical analysis lexing , syntax analysis parsing , compilation, execution. Lexical analysis Lexing Sometimes also called tokenizing, it is a phase that literally consists of converting a string of characters from the source code written in PHP into a sequence of tokens that describe what each subsequent encountered value means.
Below is an example dump provided by the VLD from a compiled Greeting class providing a sayhello method: Class Greeting: Function sayhello: number of ops: 8 compiled vars:! Defined here is the class and method, followed by: assumption of value by the function creation of the temporary variable concatenation of the strings behind the variables printing the temporary variable return from the function after its completion Describing the entire issue of OPCode and its components exhaustively would definitely go beyond the scope of this article.
Execution This is the last phase of the interpretation process.
0コメント