更新生成器类型加载器，减少重复代码，优化代码结构，更新文档。 (overtrue#78)

* 更新生成器类型加载器，减少重复代码，优化代码结构，更新文档。

* 删除没必要存在的变量～

README.md

@@ -19,19 +19,23 @@ composer require "overtrue/pinyin:~3.0"
 
 ## 使用
 
-可选两种转换方案：
+可选转换方案：
 
     - 内存型，适用于服务器内存空间较富余，优点：转换快
     - 小内存型(默认)，适用于内存比较紧张的环境，优点：占用内存小，转换不如内存型快
+    - I/O型，适用于虚拟机，内存限制比较严格环境。优点：非常微小内存消耗。缺点：转换慢，不如内存型转换快,php >= 5.5
 
 ### 拼音数组
 
 ```php
 use Overtrue\Pinyin\Pinyin;
 
-$pinyin = new Pinyin();  // 小内存型(默认)
-// 或者
-$pinyin = new Pinyin('Overtrue\Pinyin\MemoryFileDictLoader'); // 内存型
+// 小内存型
+$pinyin = new Pinyin(); // 默认
+// 内存型
+// $pinyin = new Pinyin('Overtrue\Pinyin\MemoryFileDictLoader');
+// I/O型
+// $pinyin = new Pinyin('Overtrue\Pinyin\GeneratorFileDictLoader');
 
 $pinyin->convert('带着希望去旅行，比到达终点更美好');
 // ["dai", "zhe", "xi", "wang", "qu", "lv", "xing", "bi", "dao", "da", "zhong", "dian", "geng", "mei", "hao"]
@@ -43,6 +47,11 @@ $pinyin->convert('带着希望去旅行，比到达终点更美好', PINYIN_ASCI
 //["dai4","zhe","xi1","wang4","qu4","lv3","xing2","bi3","dao4","da2","zhong1","dian3","geng4","mei3","hao3"]
 ```
 
+- 小内存型: 将字典分片载入内存
+- 内存型: 将所有字典预先载入内存
+- I/O型: 不载入内存，将字典使用文件流打开逐行便利并运用php5.5生成器(yield)特性分配单行内存
+
+
 选项：
 
 |      选项      | 描述                                                |

src/GeneratorFileDictLoader.php

@@ -11,6 +11,7 @@
 use Closure;
 use Exception;
 use SplFileObject;
+use Generator;
 
 /**
  * Generator syntax(yield) Dict File loader.
@@ -36,7 +37,14 @@ class GeneratorFileDictLoader implements DictLoaderInterface
      *
      * @var array
      */
-    protected $handles = [];
+    protected static $handles = [];
+
+    /**
+     * surnames.
+     *
+     * @var SplFileObject
+     */
+    protected static $surnamesHandle;
 
     /**
      * Constructor.
@@ -51,7 +59,7 @@ public function __construct($path)
             $segment = $this->path.'/'.sprintf($this->segmentName, $i);
 
             if (file_exists($segment) && is_file($segment)) {
-                array_push($this->handles, $this->openFile($segment));
+                array_push(static::$handles, $this->openFile($segment));
             }
         }
     }
@@ -91,28 +99,40 @@ protected function getGenerator(array $handles)
     }
 
     /**
-     * Load dict.
+     * Traverse the stream.
      *
+     * @param Generator $generator
      * @param Closure $callback
+     * @author Seven Du <[email protected]>
      */
-    public function map(Closure $callback)
+    protected function traversing(Generator $generator, Closure $callback)
     {
-        foreach ($this->getGenerator($this->handles) as $string => $pinyin) {
+        foreach ($generator as $string => $pinyin) {
             $callback([$string => $pinyin]);
         }
     }
 
+    /**
+     * Load dict.
+     *
+     * @param Closure $callback
+     */
+    public function map(Closure $callback)
+    {
+        $this->traversing($this->getGenerator(static::$handles), $callback);
+    }
+
     /**
      * Load surname dict.
      *
      * @param Closure $callback
      */
     public function mapSurname(Closure $callback)
     {
-        $surnames = $this->path.'/surnames';
-
-        foreach ($this->getGenerator([ $this->openFile($surnames) ]) as $string => $pinyin) {
-            $callback([$string => $pinyin]);
+        if (!static::$surnamesHandle instanceof SplFileObject) {
+            static::$surnamesHandle = $this->openFile($this->path.'/surnames');
         }
+
+        $this->traversing($this->getGenerator([static::$surnamesHandle]), $callback);
     }
 }