# PSR-4——新鲜出炉的PHP规范

[FIG][0] 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][1] 。

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。

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:

register();
*
* // register the base directories for the namespace prefix
* $loader->addNamespace(‘Foo\Bar’, ‘/path/to/packages/foo-bar/src’);
* $loader->addNamespace(‘Foo\Bar’, ‘/path/to/packages/foo-bar/tests’);
*
* The following line would cause the autoloader to attempt to load the
* \Foo\Bar\Qux\Quux class from /path/to/packages/foo-bar/src/Qux/Quux.php:
*
* prefixes[$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

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。

– – –

撰文SegmentFault

[0]: http://www.php-fig.org/
[1]: https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-4-autoloader.md