Objective C--解释器模式

灰太狼 2021-11-09 01:48 224阅读 0赞

首先介绍一下解释器模式适合解决哪类问题。

其实，解释器模式需要解决的问题是，如果一种特定类型的问题发生的频率足够高，那么可能就值得将该问题的各个实例表述为一个简单语言的句子。这样就可以构建一个解释器，该解释器通过解释这些句子来解决该问题。

就应用的例子来说，例如正则表达式就是它的一种具体应用，解释器可以为正则表示定义一个文法，如何表示一个特定的正则表达式，以及如何解释这个正则表达式。

下面给出解释器模式的定义。

** 解释器模式 (interpreter)，给定一个语言，定义它的文法的一种表示，并定义一个解释器，这个解释器使用该表示来解释语言中的句子。**

解释器模式的类结构图如下。

![9EB9B954583B8A1720D622BFBB8E9A7E_500_333.jpg][]

图中的结构也比较好理解，解释器方法抽象出一个统一的接口(AbstractExpression)，于需要解释的内容(Context)做了解耦，调用时为具体的解释器方法传入内容(Context)从而实现相应的解释功能。

那么解释器模式有什么好处呢？

其实用了解释器模式，就意味着可以很容易地改变和扩展文法，因为该模式使用类来表示文法规则，你可以使用继承来改变或扩展该文法。也比较容易实现文法，因为定义抽象语法树中各个节点的类的实现大体类似，这些类都易于直接编写。

那么除了之前提到的正则表达式这种应用之外，其实用处还是很广的，当然了主要还是对文本的解释。

除了好处，其实解释器模式还是有不足的，解释器模式为文法中的每一条规则至少定义了一个类，因此包含许多规则的文法可能难以管理和维护。建议当文法非常复杂时，使用其他的技术如语法分析程序或编译器生成器来处理。

说了不少，下面用代码简单展示一下解释器模式的具体实现。

==============================================

*  Context类接口

*  Context类实现

*  AbstractExpression类接口

*  AbstractExpression类实现

*  TerminalExpression类接口

*  TerminalExpression类实现

*  NonterminalExpression类接口

*  NonterminalExpression类实现

*  Main方法调用

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     <div style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;border:0px;"> 
      <code style="font-size:1em;background-image:none;vertical-align:baseline;color:#808080;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">#import "Context.h"</code> 
     </div> 
     <div style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;border:0px;"> 
      <code style="font-size:1em;background-image:none;vertical-align:baseline;color:#808080;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">#import "TerminalExpression.h"</code> 
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     <div style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;border:0px;"> 
      <code style="font-size:1em;background-image:none;vertical-align:baseline;color:#808080;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">#import "NonterminalExpression.h"</code> 
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     <div style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;border:0px;"> 
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      <code style="font-weight:bold;font-size:1em;background-image:none;vertical-align:baseline;color:#006699;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">@autoreleasepool</code> 
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      <code style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">Context *context = [[Contextalloc]init];</code> 
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      <code style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">*list = [[</code> 
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      <code style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">[list addObject:[[TerminalExpressionalloc]init]];</code> 
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     <div style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;border:0px;"> 
      <code style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">[list addObject:[[NonterminalExpressionalloc]init]];</code> 
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      <code style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">[list addObject:[[TerminalExpressionalloc]init]];</code> 
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      <code style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">[list addObject:[[TerminalExpressionalloc]init]];</code> 
     </div> 
     <div style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;border:0px;"> 
      <code style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="font-weight:bold;font-size:1em;background-image:none;vertical-align:baseline;color:#006699;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">for</code> 
      <code style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">(AbstractExpression *exp in list) { </code> 
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      <code style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">[exp Interpret:context];</code> 
     </div> 
     <div style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;border:0px;"> 
      <code style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">}</code> 
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      <code style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">}</code> 
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     <div style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;border:0px;"> 
      <code style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">&nbsp;&nbsp;&nbsp;</code> 
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      <code style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">0;</code> 
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      <code style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;font-family:Consolas, 'Bitstream Vera Sans Mono', 'Courier New', Courier, monospace;border:0px;">}</code> 
     </div> 
     <div style="font-size:1em;background-image:none;vertical-align:baseline;line-height:1.1em;border:0px;"> 
      <span style="color:#333333;font-family:Georgia;"><a href="http://www.devdiv.com/Objective_C--%E8%A7%A3%E9%87%8A%E5%99%A8%E6%A8%A1%E5%BC%8F-weblog-206180-11992.html" rel="nofollow">http://www.devdiv.com/Objective_C--%E8%A7%A3%E9%87%8A%E5%99%A8%E6%A8%A1%E5%BC%8F-weblog-206180-11992.html</a></span> 
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转载于:https://www.cnblogs.com/1208/archive/2012/08/17/2643593.html

[9EB9B954583B8A1720D622BFBB8E9A7E_500_333.jpg]: http://m1.img.libdd.com/farm3/126/9EB9B954583B8A1720D622BFBB8E9A7E_500_333.jpg