Question

我正在尝试创建一个带有字符串修剪功能的类：

Object subclass: Trimmer [
    trimleading: str [ |ch ret|
        ch := (str first: 1).           "get first character"
        ret := str.                     "make a copy of sent string"
        [ch = ' '] whileTrue: [         "while first char is space"
            ret := (ret copyFrom: 2).   "copy from 2nd char"
            ch := ret first: 1.         "again test first char"
            ].
        ^ret                            "return value is modified string"
        ].
    trim: str [ |ret|
        ret := str. 
        ret := (trimleading value: ret).           "trim leading spaces"
        ret := (trimleading value: (ret reverse)). "reverse string and repeat trim leading"
        ^(ret reverse)                             "return reverse string"
        ]
].

oristr := '        this is a test  '
('ORI..>>',oristr,'<<') displayNl.
('FINAL>>',((Trimmer new) trim: oristr),'<<') displayNl.

但是，它没有运行并给出以下错误：

$ gst trimstring_class.st

trimstring_class.st:10: invalid class body element
trimstring_class.st:17: expected expression

问题出在哪里，如何解决？

如果我在整理方法块之后删除了.，如以下代码所示：

Object subclass: Trimmer [
    trimleading: str [ |ch ret flag|
        ret := str.                     "make a copy of sent string"
        flag := true.
        [flag] whileTrue: [         "while first char is space"
            ch := ret first: 1.         "again test first char"
            ch = ' '
            ifTrue: [ ret := (ret copyFrom: 2 to: ret size)]    "copy from 2nd char"
            ifFalse: [flag := false] 
            ].
        ^ret                                "value is modified string"
        ]     "<<<<<<< PERIOD/DOT REMOVED FROM HERE."
    trim: str [ |ret|
        ret := str. 
        ret := (trimleading value: ret).           "trim leading spaces"
        ret := (trimleading value: (ret reverse)). "reverse string and repeat trim leading"
        ^(ret reverse)                      "return reverse string"
        ]
].

然后代码开始运行，但由于以下错误而停止：

$ gst trimstring_class.st 
trimstring_class.st:15: undefined variable trimleading referenced
ORI..>>        this is a test  <<
Object: Trimmer new "<0x7f1c787b4750>" error: did not understand #trim:
MessageNotUnderstood(Exception)>>signal (ExcHandling.st:254)
Trimmer(Object)>>doesNotUnderstand: #trim: (SysExcept.st:1448)
UndefinedObject>>executeStatements (trimstring_class.st:23)

为什么现在trimleading方法尚未定义，为什么要使用gnu-smalltalk did not understand #trim:？

Answer 1

通常，对于这种常见用例，检查是否已实现这种功能是明智的。您可以从中汲取灵感来编写代码（作为Smalltalk程序员，您也将得到改善）。看看sports.st中的trimBlanksFrom:：

 SpStringUtilities class >> trimBlanksFrom: aString [
    "^a String
     I return a copy of aString with all leading and trailing blanks removed."

    <category: 'services'>
    | first last |
    first := 1.
    last := aString size.
    [last > 0 and: [(aString at: last) isSeparator]] 
        whileTrue: [last := last - 1].
    ^last == 0 
        ifTrue: [String new]
        ifFalse: [
            [first < last and: [(aString at: first) isSeparator]] 
                whileTrue: [first := first + 1].
            aString copyFrom: first to: last
       ]
]

如果您只想修剪前导空格，则可以选择第二部分，它是在修剪前导空格。

编辑：OP自身的代码已修复：

Object subclass: Trimmer [
    trimleading: str [ |ch ret flag|
        ret := str.                     "make a copy of sent string"
        flag := true.
        [flag] whileTrue: [         "while first char is space"
            ch := ret first: 1.         "again test first char"
            ch = ' '
            ifTrue: [ ret := (ret copyFrom: 2 to: ret size) ]    "copy from 2nd char"
            ifFalse:  [flag := false ] 
            ].
        ^ret                                "value is modified string"
        ]     "<<<<<<< PERIOD/DOT REMOVED FROM HERE."
    trim: str [ |ret|
        ret := str. 
        ret := self trimleading: (ret copy).           "trim leading spaces"
        ret := self trimleading: (ret copy reverse). "reverse string and repeat trim leading"
        ^ (ret reverse)                      "return reverse string"
        ]
].

oristr := '        this is a test  '
('ORI..>>',oristr,'<<') displayNl.
('FINAL>>',((Trimmer new) trim: oristr),'<<') displayNl.

有一些错误需要纠正。如果要寻址选择器#trimleading:，则必须使用self关键字来搜索本地类（查找自己的类或继承的类）。接下来，您不应更改分配给您的变量，而应使用#copy，否则可能会导致奇怪的结果。

甚至没有开始修剪字符串的类和方法

1 个答案: