Question

I have a simple class. And I have to add some conditions to some methods and properties. For example:

public class Example
{
  public Boolean Condition {get; set;}
  public Double ConditionValue {get; set;}

  [Verify("!Condition && ConditionValue>5")]
  public void DoSomthing()
  { ... }
}

I want to check the condition (for example, “!Condition && ConditionValue>5”) in an aspect attribute. I can not give an action/func into an attribute so I give a simple string. And I need to translate this string into a condition:

[Serializable]
public class MyAspectAttribute : OnMethodBoundaryAspect
{
    public override void OnExit(MethodExecutionArgs args)
    {
        if (!this.Condition && this.ConditionValue>5) // If-statment from string, this is the problem...
        { ... }
    }
}  

How I can extract real if-statment from string? I see some solutions, but I’m not sure they fine:

1. Use a runtime compiler, e.g. CSharpCodeProvider.
2. Use a library such as http://flee.codeplex.com/
3. Somthing else…?

How I can do it gracefully? Thanks!

Upd: I have edited the question on the advices…
Upd2: I don’t try to verification my code, I can do this:

public class Example2
    {
      public Boolean Condition {get; set;}

      [LoggingIf("Condition")]
      public void DoSomthing1()
      { ... }

      [PrintReportIf("!Condition")]
      public void DoSomthing2()
      { ... }
    }

Answer 1

Considered using lambda expressions parser? You should be able to do something along the lines:

[Verify("(Example e) => !e.Condition && e.Condition > 5")]
public void DoSomthing() 
{ ... }

And compile that later using:

[Serializable]
public class MyAspectAttribute : OnMethodBoundaryAspect
{
    public override void OnExit(MethodExecutionArgs args)
    {
         ExprParser parser = new ExprParser();
         LambdaExpression lambda = parser.Parse(/* Verify string comes here */);
         bool isConditionMet = (bool) parser.Run(lambda, this);

         if (isConditionMet)
         { ... }
    }
}

Edit:

For custom user types, you need to provide namespace (and assembly if type resides in different assembly than the one you call parser from):

ExprParser.Using.Add("PersonTypeNamespace");
ExprParser parser = new ExprParser();
LambdaExpression lambda = parser.Parse("(Person p) => p.Name");
var output = parser.Run(lambda, new Person { Name = "DragonFire" });

In download section there’s User guide file – it provides some extra information on library usage.