Question

我想在c＃中实现像编译器这样的范围变量知道变量在哪里定义。我的意思是，像

int a = 5;
for (int i = 0; i < a; i++)
{  
   // Here you can use a variable after instantiating it, "a" can still be used
   int b = 10;
}
// b cannot be used here.

我想用xml文件来做。像

<block>
   <if> 
      <eq>
         <makevar var='var1'>somevalue</makevar>
         <makevar var='var2'>somevalue</makevar>
      </eq>
    </if>
    <get var ='var1' />
</block>

此命令<get var='var1' />无法使用，因为它不在其指定的范围内。

我该如何实现？

Answer 1

问题有点模糊，但据我所知，你想在循环中为b分配一些东西，并希望能够在循环后读取它。对此的解决方案实际上非常简单：将变量b取出循环范围。

int a = 5;
int b = 0;

for (int i = 0; i < a; i++)
{  
   // Here you can use a and b, or declare a new variable only existing within this scope
   b = 10;
}

// b is now usable everywhere within the class

Answer 2

在遍历XML时，您可以跟踪范围变量。 'makevar'元素会将变量添加到直接父级的范围。我在你的例子中添加了评论以表明这个想法：

<block> <!-- block.scope="" -->
   <if> <!-- if.scope=block.scope=="" -->
      <eq> <!-- eq.scope=if.scope=="" -->
         <!-- makevar.scope=eq.scope=="";eq.scope.add(var1) -->
         <makevar var='var1'>somevalue</makevar> 
         <!-- makevar.scope=eq.scope=="var1";eq.scope.add(var2) -->
         <makevar var='var2'>somevalue</makevar> 
         <get var ='var1'/> <!-- get.scope=eq.scope=="var1,var2" -->
      </eq>
    </if>
    <get var ='var1'/> <!-- get.scope=block.scope=="" -->
</block>

通常在输入child时 - 将其范围设置为parent（不更改父范围）。当元素为makevar时 - 将此var添加到包含当前makevar的元素范围。

修改即可。更改上面的示例以更准确地显示想法。

Answer 3

我知道我不应该，但我有空闲时间; - ）

这是一个如何解决它的建议。它既不完整也没有真正优化或安全。它的目的是为您提供一些东西。您的问题是关于范围的，因此以下代码首先进行范围检查。

它是如何工作的？每个节点（元素）由一个为其提供特殊功能的类表示。每个节点但变量也是一个可以维护子块及其变量的块。在解析期间，通过搜索xml树来检查变量的范围，如果变量属于self或parent节点并且在self之前。

我已经优化了你的xml。

<强>程序：

class Program
{
    static void Main(string[] args)
    {
        var xDoc = XDocument.Parse(xml);
        var block = new Block(xDoc.Root);
    }

    // These lines will cause an exception because both variables are out of scope.
    // <add arg1='a' arg2='b' />
    // <add arg1='a' arg2='d' />

    static string xml = @"
        <block>
            <var name='a'>2</var>
            <if condition='true'> 
                <var name='b'>3</var>
            </if>
            <var name='c'>2</var>
            <add arg1='a' arg2='a' />
            <add arg1='a' arg2='b' />
            <add arg1='a' arg2='c' />
            <add arg1='a' arg2='d' />
            <var name='d'>4</var>
        </block>";
}

BlockBase ＆amp;＆amp;的 Block ：

// Provides common functionality for blocks. abstract class BlockBase { protected BlockBase() { Variables = new List<Variable>(); Blocks = new List<BlockBase>(); } protected BlockBase(XElement xBlock) : this() { // Add variables and blocks. foreach (var item in xBlock.Elements()) { AddVariable(Variable.Parse(item)); AddBlock(IfStatement.Parse(item)); AddBlock(Addition.Parse(item)); } } BlockBase Parent { get; set; } // Block variables. public List<Variable> Variables { get; set; } // Sub-blocks. public List<BlockBase> Blocks { get; set; } // Adds a variable. private void AddVariable(Variable variable) { if (variable != null) { Variables.Add(variable); } } // Adds a block. private void AddBlock(BlockBase block) { if (block != null) { block.Parent = this; Blocks.Add(block); } } // Get a variable. public Variable GetVariable(string name) { BlockBase block = this; do { Variable variable = block.Variables.Where(x => x.Name == name).FirstOrDefault(); if (variable != null) { return variable; } block = block.Parent; } while (block != null); return null; } // Checks if variable is in scope. protected bool IsInScope(XElement xElm, string varName) { // Traverses the tree and searches for variables in parent blocks and before self // so that we don't get variables defined after self. var xCurrentElm = xElm; do { var variable = xCurrentElm .ElementsBeforeSelf() .Where(x => x.Name.LocalName == "var" && x.Attribute("name").Value == varName) .FirstOrDefault(); if (variable != null) return true; xCurrentElm = xCurrentElm.Parent; } while (xCurrentElm != null); return false; } } // Block class. class Block : BlockBase { public Block(XElement xBlock) : base(xBlock) { } }

<强> IfStatement ：

// An if-statement. class IfStatement : BlockBase { private IfStatement(XElement xIf) : base(xIf) { Condition = xIf.Attribute("condition").Value; } public static IfStatement Parse(XElement xIf) { if (xIf.Name.LocalName != "if") { return null; } return new IfStatement(xIf); } public string Condition { get; set; } // Evaluates the condition. public bool Evaluate() { return bool.Parse(Condition); } }

Addition 作为实际使用变量的内容：

// Addition block. class Addition : BlockBase { private Addition(XElement xAddition) { Arg1 = xAddition.Attribute("arg1").Value; Arg2 = xAddition.Attribute("arg2").Value; if (!IsInScope(xAddition, Arg1)) { throw new ArgumentOutOfRangeException("Arg1", String.Format("{0} is out of scope.", Arg1)); } if (!IsInScope(xAddition, Arg2)) { throw new ArgumentOutOfRangeException("Arg2", String.Format("{0} is out of scope.", Arg2)); } } public static Addition Parse(XElement xAddition) { if (xAddition.Name.LocalName != "add") { return null; } return new Addition(xAddition); } public string Arg1 { get; set; } public string Arg2 { get; set; } public int? Result { get; set; } // Evaluates the addition. public void Evaluate() { Variable arg1 = GetVariable(Arg1); Variable arg2 = GetVariable(Arg2); if (arg1 == null) { throw new ArgumentNullException("arg1"); } if (arg2 == null) { throw new ArgumentNullException("arg2"); } Result = int.Parse(arg1.Value) + int.Parse(arg2.Value); } }

<强> Variable ：

// Variable. class Variable { private Variable(XElement xVariable) { Name = xVariable.Attribute("name").Value; Value = xVariable.Value; } public static Variable Parse(XElement xVariable) { if (xVariable.Name.LocalName != "var") { return null; } return new Variable(xVariable); } public string Name { get; set; } public string Value { get; set; } }

编译器如何知道范围变量

3 个答案: