CoffeeScript 修饰模式

修饰模式

问题

你有一组数据，需要在多个过程、可能变换的方式下处理。

解决方案

使用修饰模式来构造如何更改应用。

miniMarkdown = (line) ->
    if match = line.match /^(#+)\s*(.*)$/
        headerLevel = match[1].length
        headerText = match[2]
        "#{headerText}"
    else
        if line.length > 0
            "#{line}"
        else
            ''
stripComments = (line) ->
    line.replace /\s*\/\/.*$/, '' # Removes one-line, double-slash C-style comments
class TextProcessor
    constructor: (@processors) ->
    reducer: (existing, processor) ->
        if processor
            processor(existing or '')
        else
            existing
    processLine: (text) ->
        @processors.reduce @reducer, text
    processString: (text) ->
        (@processLine(line) for line in text.split("\n")).join("\n")
exampleText = '''
              # A level 1 header
              A regular line
              // a comment
              ## A level 2 header
              A line // with a comment
              '''
processor = new TextProcessor [stripComments, miniMarkdown]
processor.processString exampleText
# => "A level 1 header\nA regular line\n\nA level 2 header\nA line"

结果

A level 1 header
A regular line
A level 1 header
A line

讨论

TextProcessor 服务有修饰的作用，可将个人、专业文本处理器绑定在一起。这使 miniMarkdown 和 stripComments 组件只专注于处理一行文本。未来的开发人员只需要编写函数返回一个字符串，并将它添加到阵列的处理器即可。

我们甚至可以修改现有的修饰对象动态：

smilies =
    ':)' : "smile"
    ':D' : "huge_grin"
    ':(' : "frown"
    ';)' : "wink"
smilieExpander = (line) ->
    if line
        (line = line.replace symbol, "") for symbol, text of smilies
    line
processor.processors.unshift smilieExpander
processor.processString "# A header that makes you :) // you may even laugh"
# => "A header that makes you "
processor.processors.shift()
# => "A header that makes you :)"