（转）lambda表达式的解析（六） 成员访问表达式

成员访问的解析稍微有点复杂，从字符串角度看，访问一个实例的成员有三种形式：

访问成员字段或属性 instance.field instance.property

访问索引器 instance[]

访问方法 instance.method(...)

在解析的时候就按这三种形式进行解析，目前由于grammar修改的不完美所以还不支持显示进行泛型方法的调用。

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  1. private Expression ProcessMemberAccessExpression(ParseTreeNode expNode)
  2. {
  3. Expression self = null;
  4. ParseTreeNode args;
  5. List<Expression> arglist;
  7. var identifier = expNode.GetDescendant("Identifier");
  8. var members = expNode.LastChild;
  9. var variableName = identifier.GetValue();
  10. var parameter = _parameters.Count > 0 ? _parameters.Peek().FirstOrDefault(p => p.Name == variableName) : null;
  11. if (parameter != null)
  12. {
  13. self = parameter;
  14. }
  15. else
  16. {
  17. var pair = _knownVariables.FirstOrDefault(p => p.Key == variableName);
  18. if (pair.Key == variableName)
  19. {
  20. self = Expression.Constant(pair.Value);
  21. //self = Expression.Variable(pair.Value.GetType(), variableName);
  22. }
  23. else if (_parameters.Count > 0)
  24. {
  25. var parameters = _parameters.Peek();
  26. var usedParameter = parameters.FirstOrDefault(p => p.Type.GetMember(variableName).Length > 0);
  27. if (usedParameter != null)
  28. self = Expression.MakeMemberAccess(usedParameter, usedParameter.Type.GetMember(variableName).First());
  29. }
  31. if (self == null)
  32. {
  33. throw new Exception(variableName);
  34. }
  35. }
  36. if (members.ChildNodes.Count == 0)
  37. {
  38. return self;
  39. }
  40. foreach (var child in members.ChildNodes)
  41. {
  42. var type = self.Type;
  43. var member = child.LastChild;
  44. MemberInfo membinfo;
  45. switch (member.GetName())
  46. {
  47. case "Identifier":
  48. membinfo = type.GetMember(member.GetValue()).First();
  49. self = Expression.MakeMemberAccess(self, membinfo);
  50. break;
  51. case "member_invoke":
  52. var methodName = member.FirstChild.GetValue();
  53. var method = type.GetMethod(methodName);
  54. args = member.GetDescendant("argument_list");
  55. arglist = new List<Expression>();
  56. if (args != null)
  57. {
  58. foreach (var arg in args.ChildNodes)
  59. {
  60. arglist.Add(ProcessExpression(arg.FirstChild));
  61. }
  62. }
  63. if (method == null)
  64. {
  65. method = MakeMethod(methodName, new[] { self.GetElementType() }.Union(arglist.Select(arg => arg.Type)).ToArray());
  66. self = Expression.Call(method, new[] { self }.Union(arglist));
  67. }
  68. else
  69. {
  70. self = Expression.Call(self, method, arglist);
  71. }
  72. break;
  73. case "member_indexer":
  74. var indexer = type.GetProperty(member.FirstChild.GetValue());
  75. args = member.GetDescendant("expression_list");
  76. arglist = new List<Expression>();
  77. foreach (var arg in args.ChildNodes)
  78. {
  79. arglist.Add(ProcessExpression(arg.FirstChild));
  80. }
  81. self = Expression.MakeIndex(self, indexer, arglist);
  82. break;
  83. default:
  84. throw new Exception(member.GetName());
  85. }
  86. }
  87. return self;
  88. }


所有访问的成员都作为子节点进行访问，而实例则是通过查找之前介绍过的_knownVariables以及_parameters获得的。

成员字段和索引器访问都是可以直接分析生成得到，成员方法的情况稍微复杂点，首先是通过Type.GetMethod查找类型下的指定方法，因为暂时不考虑泛型方法，所以找到后就直接生成表达式不需要做MakeGenericMethod操作。假如没有找到同名方法的话，则直接推断为该方法是一个扩展方法，进行扩展方法调用，代码里对扩展方法的处理方式是事先注册好扩展方法，然后按名字查找对应的方法进行使用。

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  1. private static ConcurrentDictionary<string, MethodInfo> extensionMethods = new ConcurrentDictionary<string, MethodInfo>();
  3. #region ExtensionMethods
  4. extensionMethods["select"] = typeof(Queryable).GetExtensionMethod("Select", typeof(IQueryable<>), typeof(Expression<>).MakeGenericType(typeof(Func<,>)));
  5. extensionMethods["let"] = extensionMethods["select"];
  6. extensionMethods["from"] = typeof(Queryable).GetExtensionMethod("SelectMany", typeof(IQueryable<>), typeof(Expression<>).MakeGenericType(typeof(Func<,>)), typeof(Expression<>).MakeGenericType(typeof(Func<,,>)));
  7. //extensionMethods["from"] = typeof(Queryable).GetMember("SelectMany")[3] as MethodInfo;
  8. extensionMethods["group"] = typeof(Queryable).GetExtensionMethod("GroupBy", typeof(IQueryable<>), typeof(Expression<>).MakeGenericType(typeof(Func<,>)));
  9. extensionMethods["join"] = typeof(Queryable).GetExtensionMethod("Join", typeof(IQueryable<>), typeof(IEnumerable<>), typeof(Expression<>).MakeGenericType(typeof(Func<,>)), typeof(Expression<>).MakeGenericType(typeof(Func<,>)), typeof(Expression<>).MakeGenericType(typeof(Func<,,>)));
  10. extensionMethods["groupjoin"] = typeof(Queryable).GetExtensionMethod("GroupJoin", typeof(IQueryable<>), typeof(IEnumerable<>), typeof(Expression<>).MakeGenericType(typeof(Func<,>)), typeof(Expression<>).MakeGenericType(typeof(Func<,>)), typeof(Expression<>).MakeGenericType(typeof(Func<,,>)));
  11. extensionMethods["orderby"] = typeof(Queryable).GetExtensionMethod("OrderBy", typeof(IQueryable<>), typeof(Expression<>).MakeGenericType(typeof(Func<,>)));
  12. extensionMethods["orderbydescending"] = typeof(Queryable).GetExtensionMethod("OrderByDescending", typeof(IQueryable<>), typeof(Expression<>).MakeGenericType(typeof(Func<,>)));
  13. extensionMethods["thenby"] = typeof(Queryable).GetExtensionMethod("ThenBy", typeof(IOrderedQueryable<>), typeof(Expression<>).MakeGenericType(typeof(Func<,>)));
  14. extensionMethods["thenbydescending"] = typeof(Queryable).GetExtensionMethod("ThenByDescending", typeof(IOrderedQueryable<>), typeof(Expression<>).MakeGenericType(typeof(Func<,>)));
  15. extensionMethods["where"] = typeof(Queryable).GetExtensionMethod("Where", typeof(IQueryable<>), typeof(Expression<>).MakeGenericType(typeof(Func<,>)));
  16. extensionMethods["DefaultIfEmpty"] = typeof(Enumerable).GetExtensionMethod("DefaultIfEmpty", typeof(IEnumerable<>));
  17. #endregion
  19. private static MethodInfo MakeMethod(string methodName, params Type[] genericTypes)
  20. {
  21. var len = extensionMethods[methodName].GetGenericArguments().Length;
  22. return extensionMethods[methodName].MakeGenericMethod(genericTypes.Take(len).ToArray());
  23. }


MakeMethod就是根据方法名和泛型列表返回相应的扩展方法，这里列出的方法都是针对linq做的，全都是泛型方法。

通过方法名和泛型列表获得一个扩展方法需要一些技巧：

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  1. internal static class TypeExtensions
  2. {
  3. private class ParameterComparer : IEqualityComparer<Type>
  4. {
  6. #region IEqualityComparer<Type> Members
  8. public bool Equals(Type x, Type y)
  9. {
  10. if (x.IsGenericParameter && y.IsGenericParameter)
  11. return true;
  13. if (x.IsGenericType && y.IsGenericType)
  14. {
  15. if (x.Name != y.Name) return false;
  16. if (x.BaseType != y.BaseType) return false;
  18. var xa = x.GetGenericArguments();
  19. var ya = y.GetGenericArguments();
  20. if (xa.Length != ya.Length) return false;
  22. var ret = xa.SequenceEqual(ya, this);
  23. return ret;
  24. }
  26. if (x.IsGenericType) return true;
  27. if (!y.IsGenericType) return true;
  29. return x.Equals(y);
  30. }
  32. public int GetHashCode(Type obj)
  33. {
  34. return obj.GetHashCode();
  35. }
  37. #endregion
  38. }
  40. public static MethodInfo GetExtensionMethod(this Type type, string name, params Type[] arguments)
  41. {
  42. var query = from method in type.GetMethods()
  43. let parameters = from p in method.GetParameters() select p.ParameterType
  44. where method.Name == name
  45. where method.IsDefined(typeof(ExtensionAttribute), false)
  46. where parameters.SequenceEqual(arguments, new ParameterComparer())
  47. select method;
  49. return query.FirstOrDefault();
  50. }
  51. }


简单点说就是通过反射获得扩展方法类下的所有方法，然后先按照名字匹配到一组方法，接着根据泛型参数来比较获得特定的那个，这里有个小的问题没解决，所以在实现IEqualityComparer<T>时代码比较冗余。小问题是

Func<T> 的泛型类型可以通过 typeof(Func<>)得到

而Func<T1,T2>泛型类型则是 typeof(Func<,>)

那么Func<T1,IEnumerable<T2>,T3>这种泛型类型如何获得？ typeof(Func<,,>)无法匹配 而typeof(Func<,IEnumerable<>,>)无法通过编译。

posted @ 2011-10-13 22:48  小芒果  阅读(635)  评论(0)  编辑  收藏  举报