(C#) 表达式树

需求是将一个string 表达式 转换成 逻辑 表达式 并得到结果。

例如： bool result = (key1==val1) || (key2!=val2) && (key3==val3). 其中 keyN, valN 均为变量。

基本的思路是先做Express string 验证，然后进行解析。

验证可以用正则表达式。

解析最基本的方法是用 表达式树 (Express Tree).  PostFix. 

C# linq 提供了一个解决方案就是 Linq 语法树。

https://www.codeproject.com/Articles/74018/How-to-Parse-and-Convert-a-Delegate-into-an-Expre

目前较好的方法是用Microsoft 的  Dynamic Linq (http://msdn.microsoft.com/en-us/vcsharp/bb894665.aspx)

static void Main(string[] args)
        {
            string[] exps = new string[]
            {
                @" ""keyA"" !=""valA"" ",
                @"keyA !=""valA""",
                @"(keyA ==""valA"")",
                @"keyA ==""val1"" || key2 ==""val2""",
                @"key1 ==""val1"" && key2 ==""val2""",
                @" key1 !=""val1"" || key2 ==""val2""&& key3 != ""val3""",
                @"(key1 ==""val1"" || key2 ==""val2"")&& key3 != ""val3""",
            };

            string pattern = @"(?<key>[wd_]+)""*s*(?<equality>==|!=)s*""*(?<value>[wd_]+)";

            foreach (var exp in exps)
            {
                // Parses to get the parameters.
                string formattedExp = exp; 
                var matches = Regex.Matches(exp, pattern);
                ParameterExpression[] parameters = new ParameterExpression[matches.Count]; 
                for (int i =0; i < matches.Count; i++)
                {
                    Debug.Write(" key[" + matches[i].Groups["key"].Value);
                    Debug.Write("] equality[" + matches[i].Groups["equality"].Value);
                    Debug.Write("] value[" + matches[i].Groups["value"].Value +"]	
");

                    parameters[i] = Expression.Parameter(typeof(string), matches[i].Groups["key"].Value);

                    // Removing " if it has in keys.
                    if (exp.Contains(string.Format(@"""{0}""", matches[i].Groups["key"].Value)))
                    {
                        formattedExp = exp.Replace(string.Format(@"""{0}""", matches[i].Groups["key"].Value), matches[i].Groups["key"].Value); 
                    }
                }

                var e = System.Linq.Dynamic.DynamicExpression.ParseLambda(parameters, null, formattedExp);

                string[] GotValues = new string[matches.Count]; 
               if (GotValues.Length == 2)
               {
                   GotValues[0] = "val1";
                   GotValues[1] = "val2";
               }

               if (GotValues.Length == 3)
               {
                   GotValues[0] = "val1";
                   GotValues[1] = "val2";
                   GotValues[2] = "val3";
               }

                var result = e.Compile().DynamicInvoke(GotValues);

                Debug.WriteLine("{0} ---> {1}", e.ToString(), result); 
            }
        }

输出如下：

 keyA => (keyA != "valA") ---> True
 key[keyA] equality[!=] value[valA] 
keyA => (keyA != "valA") ---> True
 key[keyA] equality[==] value[valA] 
keyA => (keyA == "valA") ---> False
 key[keyA] equality[==] value[val1] 
 key[key2] equality[==] value[val2] 
(keyA, key2) => ((keyA == "val1") OrElse (key2 == "val2")) ---> True
 key[key1] equality[==] value[val1] 
 key[key2] equality[==] value[val2] 
(key1, key2) => ((key1 == "val1") AndAlso (key2 == "val2")) ---> True
 key[key1] equality[!=] value[val1] 
 key[key2] equality[==] value[val2] 
 key[key3] equality[!=] value[val3] 
(key1, key2, key3) => ((key1 != "val1") OrElse ((key2 == "val2") AndAlso (key3 != "val3"))) ---> False
 key[key1] equality[==] value[val1] 
 key[key2] equality[==] value[val2] 
 key[key3] equality[!=] value[val3] 
(key1, key2, key3) => (((key1 == "val1") OrElse (key2 == "val2")) AndAlso (key3 != "val3")) ---> False

 参考：

https://stackoverflow.com/questions/821365/how-to-convert-a-string-to-its-equivalent-linq-expression-tree