PSR-4——新鲜出炉的PHP规范

小鱼儿 2022-07-24 06:21 379阅读 0赞

[FIG][]制定的PHP规范，简称PSR，是PHP开发的事实标准。

PSR原本有四个规范，分别是：

*  PSR-0 自动加载
 *  PSR-1 基本代码规范
 *  PSR-2 代码样式
 *  PSR-3 日志接口

2013年底，新出了第5个规范——[PSR-4][]。

PSR-4规范了如何指定文件路径从而自动加载类定义，同时规范了自动加载文件的位置。这个乍一看和PSR-0重复了，实际上，在功能上确实有所重复。区别在于PSR-4的规范比较干净，去除了兼容PHP 5.3以前版本的内容，有一点PSR-0升级版的感觉。当然，PSR-4也不是要完全替代PSR-0，而是在必要的时候补充PSR-0——当然，如果你愿意，PSR-4也可以替代PSR-0。PSR-4可以和包括PSR-0在内的其他自动加载机制共同使用。

PSR-4和PSR-0最大的区别是对下划线（underscore)的定义不同。PSR-4中，在类名中使用下划线没有任何特殊含义。而PSR-0则规定类名中的下划线`_`会被转化成目录分隔符。

## 代码样例 ##

以下代码展示了遵循PSR-4的类定义，这个类处理多个命名空间：

<?php
    namespace Example;
    
    /** * An example of a general-purpose implementation that includes the optional * functionality of allowing multiple base directories for a single namespace * prefix. * * Given a foo-bar package of classes in the file system at the following * paths ... * * /path/to/packages/foo-bar/ * src/ * Baz.php # Foo\Bar\Baz * Qux/ * Quux.php # Foo\Bar\Qux\Quux * tests/ * BazTest.php # Foo\Bar\BazTest * Qux/ * QuuxTest.php # Foo\Bar\Qux\QuuxTest * * ... add the path to the class files for the \Foo\Bar\ namespace prefix * as follows: * * <?php * // instantiate the loader * $loader = new \Example\Psr4AutoloaderClass; * * // register the autoloader * $loader->register(); * * // register the base directories for the namespace prefix * $loader->addNamespace('Foo\Bar', '/path/to/packages/foo-bar/src'); * $loader->addNamespace('Foo\Bar', '/path/to/packages/foo-bar/tests'); * * The following line would cause the autoloader to attempt to load the * \Foo\Bar\Qux\Quux class from /path/to/packages/foo-bar/src/Qux/Quux.php: * * <?php * new \Foo\Bar\Qux\Quux; * * The following line would cause the autoloader to attempt to load the * \Foo\Bar\Qux\QuuxTest class from /path/to/packages/foo-bar/tests/Qux/QuuxTest.php: * * <?php * new \Foo\Bar\Qux\QuuxTest; */
    class Psr4AutoloaderClass {
        /** * An associative array where the key is a namespace prefix and the value * is an array of base directories for classes in that namespace. * * @var array */
        protected $prefixes = array();
    
        /** * Register loader with SPL autoloader stack. * * @return void */
        public function register() {
            spl_autoload_register(array($this, 'loadClass'));
        }
    
        /** * Adds a base directory for a namespace prefix. * * @param string $prefix The namespace prefix. * @param string $base_dir A base directory for class files in the * namespace. * @param bool $prepend If true, prepend the base directory to the stack * instead of appending it; this causes it to be searched first rather * than last. * @return void */
        public function addNamespace($prefix, $base_dir, $prepend = false) {
            // normalize namespace prefix
            $prefix = trim($prefix, '\\') . '\\';
    
            // normalize the base directory with a trailing separator
            $base_dir = rtrim($base_dir, '/') . DIRECTORY_SEPARATOR;
            $base_dir = rtrim($base_dir, DIRECTORY_SEPARATOR) . '/';
    
            // initialize the namespace prefix array
            if (isset($this->prefixes[$prefix]) === false) {
                $this->prefixes[$prefix] = array();
            }
    
            // retain the base directory for the namespace prefix
            if ($prepend) {
                array_unshift($this->prefixes[$prefix], $base_dir);
            } else {
                array_push($this->prefixes[$prefix], $base_dir);
            }
        }
    
        /** * Loads the class file for a given class name. * * @param string $class The fully-qualified class name. * @return mixed The mapped file name on success, or boolean false on * failure. */
        public function loadClass($class) {
            // the current namespace prefix
            $prefix = $class;
    
            // work backwards through the namespace names of the fully-qualified
            // class name to find a mapped file name
            while (false !== $pos = strrpos($prefix, '\\')) {
    
                // retain the trailing namespace separator in the prefix
                $prefix = substr($class, 0, $pos + 1);
    
                // the rest is the relative class name
                $relative_class = substr($class, $pos + 1);
    
                // try to load a mapped file for the prefix and relative class
                $mapped_file = $this->loadMappedFile($prefix, $relative_class);
                if ($mapped_file) {
                    return $mapped_file;
                }
    
                // remove the trailing namespace separator for the next iteration
                // of strrpos()
                $prefix = rtrim($prefix, '\\');   
            }
    
            // never found a mapped file
            return false;
        }
    
        /** * Load the mapped file for a namespace prefix and relative class. * * @param string $prefix The namespace prefix. * @param string $relative_class The relative class name. * @return mixed Boolean false if no mapped file can be loaded, or the * name of the mapped file that was loaded. */
        protected function loadMappedFile($prefix, $relative_class) {
            // are there any base directories for this namespace prefix?
            if (isset($this->prefixes[$prefix]) === false) {
                return false;
            }
    
            // look through base directories for this namespace prefix
            foreach ($this->prefixes[$prefix] as $base_dir) {
    
                // replace the namespace prefix with the base directory,
                // replace namespace separators with directory separators
                // in the relative class name, append with .php
                $file = $base_dir
                      . str_replace('\\', DIRECTORY_SEPARATOR, $relative_class)
                      . '.php';
                $file = $base_dir
                      . str_replace('\\', '/', $relative_class)
                      . '.php';
    
                // if the mapped file exists, require it
                if ($this->requireFile($file)) {
                    // yes, we're done
                    return $file;
                }
            }
    
            // never found it
            return false;
        }
    
        /** * If a file exists, require it from the file system. * * @param string $file The file to require. * @return bool True if the file exists, false if not. */
        protected function requireFile($file) {
            if (file_exists($file)) {
                require $file;
                return true;
            }
            return false;
        }
    }

相应的单元测试代码

<?php
    namespace Example\Tests;
    
    class MockPsr4AutoloaderClass extends Psr4AutoloaderClass {
        protected $files = array();
    
        public function setFiles(array $files) {
            $this->files = $files;
        }
    
        protected function requireFile($file) {
            return in_array($file, $this->files);
        }
    }
    
    class Psr4AutoloaderClassTest extends \PHPUnit_Framework_TestCase {
        protected $loader;
    
        protected function setUp() {
            $this->loader = new MockPsr4AutoloaderClass;
    
            $this->loader->setFiles(array(
                '/vendor/foo.bar/src/ClassName.php',
                '/vendor/foo.bar/src/DoomClassName.php',
                '/vendor/foo.bar/tests/ClassNameTest.php',
                '/vendor/foo.bardoom/src/ClassName.php',
                '/vendor/foo.bar.baz.dib/src/ClassName.php',
                '/vendor/foo.bar.baz.dib.zim.gir/src/ClassName.php',
            ));
    
            $this->loader->addNamespace(
                'Foo\Bar',
                '/vendor/foo.bar/src'
            );
    
            $this->loader->addNamespace(
                'Foo\Bar',
                '/vendor/foo.bar/tests'
            );
    
            $this->loader->addNamespace(
                'Foo\BarDoom',
                '/vendor/foo.bardoom/src'
            );
    
            $this->loader->addNamespace(
                'Foo\Bar\Baz\Dib',
                '/vendor/foo.bar.baz.dib/src'
            );
    
            $this->loader->addNamespace(
                'Foo\Bar\Baz\Dib\Zim\Gir',
                '/vendor/foo.bar.baz.dib.zim.gir/src'
            );
        }
    
        public function testExistingFile() {
            $actual = $this->loader->loadClass('Foo\Bar\ClassName');
            $expect = '/vendor/foo.bar/src/ClassName.php';
            $this->assertSame($expect, $actual);
    
            $actual = $this->loader->loadClass('Foo\Bar\ClassNameTest');
            $expect = '/vendor/foo.bar/tests/ClassNameTest.php';
            $this->assertSame($expect, $actual);
        }
    
        public function testMissingFile() {
            $actual = $this->loader->loadClass('No_Vendor\No_Package\NoClass');
            $this->assertFalse($actual);
        }
    
        public function testDeepFile() {
            $actual = $this->loader->loadClass('Foo\Bar\Baz\Dib\Zim\Gir\ClassName');
            $expect = '/vendor/foo.bar.baz.dib.zim.gir/src/ClassName.php';
            $this->assertSame($expect, $actual);
        }
    
        public function testConfusion() {
            $actual = $this->loader->loadClass('Foo\Bar\DoomClassName');
            $expect = '/vendor/foo.bar/src/DoomClassName.php';
            $this->assertSame($expect, $actual);
    
            $actual = $this->loader->loadClass('Foo\BarDoom\ClassName');
            $expect = '/vendor/foo.bardoom/src/ClassName.php';
            $this->assertSame($expect, $actual);
        }
    }

## Composer ##

PHP的包管理系统[Composer][]已经支持PSR-4，同时也允许在`composer.json`中定义不同的prefix使用不同的自动加载机制。

Composer使用PSR-0风格

vendor/
        vendor_name/
            package_name/
                src/
                    Vendor_Name/
                        Package_Name/
                            ClassName.php       # Vendor_Name\Package_Name\ClassName
                tests/
                    Vendor_Name/
                        Package_Name/
                            ClassNameTest.php   # Vendor_Name\Package_Name\ClassName

Composer使用PSR-4风格

vendor/
        vendor_name/
            package_name/
                src/
                    ClassName.php       # Vendor_Name\Package_Name\ClassName
                tests/
                    ClassNameTest.php   # Vendor_Name\Package_Name\ClassNameTest

对比以上两种结构，明显可以看出PSR-4带来更简洁的文件结构。

[FIG]: http://www.php-fig.org/
[PSR-4]: https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-4-autoloader.md
[Composer]: http://segmentfault.com/a/1190000000353129