WinRT C＃动态表达式评估器

Question

There is a requirement in my application to evaluate string expressions during runtime in WinRT c# application.

Here are some example expressions:

strObj.Substring(10) + strObj.Substring(strObj.Length - 3) 
'001' + strObj.Substring(3) + '003'

Note: Above expressions will be defined in the backend and the application should evaluate at runtime with users input.

I looked at DynamicExpresso, NReco and some other expression evaluators none of those works in WinRT environment. Is there any framework available in WinRT? or how can I achieve it in code?

Answer 1

WinRT environment cannot reference usual class library until it compiled as portable class library (PCL). Portable libraries have a lot of restrictions on framework classes/methods usage (only subset of usual .NET classes is allowed); in most cases class library cannot be compiled as PCL without additional adoption for these restrictions.

I've investigated possibility of compiling NReco LambdaParser as PCL and got positive results. PCL-adopted version doesn't include flexible NReco Type Converters (they are based on ITypeConverter/TypeDescriptor which are not available for PCL) and use just Convert.ChangeType instead.

Download link: NReco LambdaParser Portable (with source code)

The following code works fine with PCL version of LambdaParser:

var lambdaParser = new LambdaParser();
Func<string,int,string> left = (s,n) => { return s.Substring(n); };
var vars = new Dictionary<string,object>() {
    {"str1", "123456"},
    {"str2", "123"},
    {"Left", left} // custom function
};
var res = lambdaParser.Eval(
    "str1.Substring(3)+\" \"+str2.Substring(str2.Length-2)+\" \"+Left(str1,1)", vars );
Console.WriteLine("Res: {0}", res);

If you found that this PCL-version is usable I may publish its source code on GitHub and create Nuget package.

Answer 2

You can also try DynLan - it also supports PCL / net3.5 / net.core ( https://github.com/byte/DynLan ). The library parses the code itself and execute it line by line. Here is small example with your expression (result == "klmnoprstuwxyzxyz"):

            var dict = new Dictionary<string, object>();
            dict["strObj"] = "abcdefghijklmnoprstuwxyz";

            object result = new Compiler().
                Compile(@" strObj.Substring(10) + strObj.Substring(strObj.Length - 3) ").
                Eval(dict);

You can also use variables inside you script, like that (result == "ABCDEPRSTU"):

            var dict = new Dictionary<string, object>();
            dict["strObj"] = "abcdefghijklmnoprstuwxyz";

            object result = new Compiler().
                Compile(
                    @" a = strObj.Substring(0, 5).ToUpper(); " +
                    @" b = strObj.Substring(15, 5).ToUpper(); " +
                    @" a + b ").
                Eval(dict);