C#中是否有方法来检查字符串是否是有效的标识符

Question

在Java中,有所谓的方法isJavaIdentifierStart和isJavaIdentifierPart对可用于判断一个字符串是一个有效的Java标识,像这样的字符类别:

public boolean isJavaIdentifier(String s) {
  int n = s.length();
  if (n==0) return false;
  if (!Character.isJavaIdentifierStart(s.charAt(0)))
      return false;
  for (int i = 1; i < n; i++)
      if (!Character.isJavaIdentifierPart(s.charAt(i)))
          return false;
  return true;
}

C#有这样的东西吗？

Answer 1

是:

// using System.CodeDom.Compiler;
CodeDomProvider provider = CodeDomProvider.CreateProvider("C#");
if (provider.IsValidIdentifier (YOUR_VARIABLE_NAME)) {
      // Valid
} else {
      // Not valid
}

从这里:如何确定字符串是否是有效的变量名称？

Answer 2

我会对这里提供的其他解决方案保持警惕.调用CodeDomProvider.CreateProvider需要查找和解析Machine.Config文件以及app.config文件.这可能比检查你自己的弦所需的时间慢几倍.

相反,我会主张你做出以下改变之一:

1. 将提供程序缓存在静态变量中.

   这将使您仅创建一次创建它,但它会减慢类型加载速度.

2. 通过创建自己的Microsoft.CSharp.CSharpCodeProvider实例直接创建提供程序

   这将跳过配置文件一起解析.

3. 编写代码来实现检查你自己.

   如果这样做,您可以最大程度地控制其实施方式,如果需要,可以帮助您优化性能.有关C#标识符的完整词法语法,请参阅C#语言规范的 2.2.4节.

Answer 3

基本上是这样的:

const string start = @"(\p{Lu}|\p{Ll}|\p{Lt}|\p{Lm}|\p{Lo}|\p{Nl})";
const string extend = @"(\p{Mn}|\p{Mc}|\p{Nd}|\p{Pc}|\p{Cf})";
Regex ident = new Regex(string.Format("{0}({0}|{1})*", start, extend));
s = s.Normalize();
return ident.IsMatch(s);

Answer 4

由于Roslyn是开源的，代码分析工具就在您的指尖，它们是为性能而编写的。（现在它们处于预发布阶段）。

但是，我无法谈论加载程序集的性能成本。

使用 nuget 安装工具：

Install-Package Microsoft.CodeAnalysis -Pre

问你的问题：

var isValid = Microsoft.CodeAnalysis.CSharp.SyntaxFacts.IsValidIdentifier("I'mNotValid");
Console.WriteLine(isValid);     // False

Answer 5

死灵法术在这里。

在 .NET Core/DNX 中，你可以使用 Roslyn-SyntaxFacts

Microsoft.CodeAnalysis.CSharp.SyntaxFacts.IsReservedKeyword(
        Microsoft.CodeAnalysis.CSharp.SyntaxFacts.GetKeywordKind("protected")
);



foreach (ColumnDefinition cl in tableColumns)
{
    sb.Append(@"         public ");
    sb.Append(cl.DOTNET_TYPE);
    sb.Append(" ");

    // for keywords
    //if (!Microsoft.CodeAnalysis.CSharp.SyntaxFacts.IsValidIdentifier(cl.COLUMN_NAME))
    if (Microsoft.CodeAnalysis.CSharp.SyntaxFacts.IsReservedKeyword(
        Microsoft.CodeAnalysis.CSharp.SyntaxFacts.GetKeywordKind(cl.COLUMN_NAME)
        ))
        sb.Append("@");

    sb.Append(cl.COLUMN_NAME);
    sb.Append("; // ");
    sb.AppendLine(cl.SQL_TYPE);
} // Next cl 

或者在 Codedom 的旧变体中 - 在查看 mono 源代码后：

CodeDomProvider.cs

public virtual bool IsValidIdentifier (string value) 
286         { 
287             ICodeGenerator cg = CreateGenerator (); 
288             if (cg == null) 
289                 throw GetNotImplemented (); 
290             return cg.IsValidIdentifier (value); 
291         } 
292  

然后 CSharpCodeProvider.cs

public override ICodeGenerator CreateGenerator() 
91      { 
92 #if NET_2_0 
93          if (providerOptions != null && providerOptions.Count > 0) 
94              return new Mono.CSharp.CSharpCodeGenerator (providerOptions); 
95 #endif 
96          return new Mono.CSharp.CSharpCodeGenerator(); 
97      } 

然后 CSharpCodeGenerator.cs

protected override bool IsValidIdentifier (string identifier)
{
    if (identifier == null || identifier.Length == 0)
        return false;

    if (keywordsTable == null)
        FillKeywordTable ();

    if (keywordsTable.Contains (identifier))
        return false;

    if (!is_identifier_start_character (identifier [0]))
        return false;

    for (int i = 1; i < identifier.Length; i ++)
        if (! is_identifier_part_character (identifier [i]))
            return false;

    return true;
}



private static System.Collections.Hashtable keywordsTable;
private static string[] keywords = new string[] {
    "abstract","event","new","struct","as","explicit","null","switch","base","extern",
    "this","false","operator","throw","break","finally","out","true",
    "fixed","override","try","case","params","typeof","catch","for",
    "private","foreach","protected","checked","goto","public",
    "unchecked","class","if","readonly","unsafe","const","implicit","ref",
    "continue","in","return","using","virtual","default",
    "interface","sealed","volatile","delegate","internal","do","is",
    "sizeof","while","lock","stackalloc","else","static","enum",
    "namespace",
    "object","bool","byte","float","uint","char","ulong","ushort",
    "decimal","int","sbyte","short","double","long","string","void",
    "partial", "yield", "where"
};


static void FillKeywordTable ()
{
    lock (keywords) {
        if (keywordsTable == null) {
            keywordsTable = new Hashtable ();
            foreach (string keyword in keywords) {
                keywordsTable.Add (keyword, keyword);
            }
        }
    }
}



static bool is_identifier_start_character (char c)
{
    return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_' || c == '@' || Char.IsLetter (c);
}

static bool is_identifier_part_character (char c)
{
    return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_' || (c >= '0' && c <= '9') || Char.IsLetter (c);
}

你得到这个代码：

public static bool IsValidIdentifier (string identifier)
{
    if (identifier == null || identifier.Length == 0)
        return false;

    if (keywordsTable == null)
        FillKeywordTable();

    if (keywordsTable.Contains(identifier))
        return false;

    if (!is_identifier_start_character(identifier[0]))
        return false;

    for (int i = 1; i < identifier.Length; i++)
        if (!is_identifier_part_character(identifier[i]))
            return false;

    return true;
}


internal static bool is_identifier_start_character(char c)
{
    return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_' || c == '@' || char.IsLetter(c);
}

internal static bool is_identifier_part_character(char c)
{
    return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_' || (c >= '0' && c <= '9') || char.IsLetter(c);
}


private static System.Collections.Hashtable keywordsTable;
private static string[] keywords = new string[] {
    "abstract","event","new","struct","as","explicit","null","switch","base","extern",
    "this","false","operator","throw","break","finally","out","true",
    "fixed","override","try","case","params","typeof","catch","for",
    "private","foreach","protected","checked","goto","public",
    "unchecked","class","if","readonly","unsafe","const","implicit","ref",
    "continue","in","return","using","virtual","default",
    "interface","sealed","volatile","delegate","internal","do","is",
    "sizeof","while","lock","stackalloc","else","static","enum",
    "namespace",
    "object","bool","byte","float","uint","char","ulong","ushort",
    "decimal","int","sbyte","short","double","long","string","void",
    "partial", "yield", "where"
};

internal static void FillKeywordTable()
{
    lock (keywords)
    {
        if (keywordsTable == null)
        {
            keywordsTable = new System.Collections.Hashtable();
            foreach (string keyword in keywords)
            {
                keywordsTable.Add(keyword, keyword);
            }
        }
    }
}