CODEWITHSUNDEEP
c#linq-expressions
toddmo
toddmo

Reputation: 22406

Error upon Expression.Lambda().Compile()

I have the following simple code:

  var b = Expression.Parameter(typeof(double), "b");
  var negativeB = Expression.Negate(b);

If I stop there and try to quick watch Expression.Lambda(negativeB).Compile() I get an error:

variable 'b' of type 'System.Double' referenced from scope '', but it is not defined

The other answers about this error message don't seem to address what's going on here, or how to fix it in this case.

Upvotes: 0

Views: 631

Answers (2)

Chris
Chris

Reputation: 27609

You have an expression negativeB that requires an input parameter of b. However when you are defining your Lambda you are not defining any parameters.

What you need to do is this:

Expression.Lambda(negativeB, b).Compile();

This then compiles

Upvotes: 3

Ofir Winegarten
Ofir Winegarten

Reputation: 9365

You should specify the parameter (b) in the Lambda:

var l = Expression.Lambda(negativeB, b).Compile();
var r = l.DynamicInvoke(32); // = -32

Upvotes: 3

Related Questions