Question

I need to translate strings like this:

"DateTime.Now.AddDays(-7)"

into their equivalent expressions.

I’m only interested in the DateTime class. Is there anything built into .Net that’ll help me do this, or do I just need to write my own little parser?

Answer 1

You can employ FLEE to do the expression parsing for you. The below code is tested and working in Silverlight (I believe in full C#, it may have a slightly different syntax around creating the expression, but it might work exactly like this anyway)

ExpressionContext context = new ExpressionContext();

//Tell FLEE to expect a DateTime result; if the expression evaluates otherwise, 
//throws an ExpressionCompileException when compiling the expression
context.Options.ResultType = typeof(DateTime);

//Instruct FLEE to expose the `DateTime` static members and have 
//them accessible via "DateTime".
//This mimics the same exact C# syntax to access `DateTime.Now`
context.Imports.AddType(typeof(DateTime), "DateTime");

//Parse the expression, naturally the string would come from your data source
IDynamicExpression expression = ExpressionFactory.CreateDynamic("DateTime.Now.AddDays(-7)", context);

//I believe there's a syntax in full C# that lets you evaluate this 
//with a generic flag, but in this build, I only have it return type 
//`Object` so we cast (it does return a `DateTime` though)
DateTime date = (DateTime)expression.Evaluate();

Console.WriteLine(date); //January 25th (7 days ago for me!)