In C#, I'm having trouble using BinaryExpression.

c# expression-trees


I want to implement

Expression<Func<int, int, int>> Max = (p1,p2) => p1 > p2 ? p1:p2;

as an expression tree and tried

ParameterExpression LeftEx = Expression.Parameter(typeof(int), "p1");
ParameterExpression RightEx = Expression.Parameter(typeof(int), "p2");
BinaryExpression GroesserAls =  Expression.GreaterThan(LeftEx, RightEx);
ConditionalExpression Cond = BinaryExpression.Condition(GroesserAls, LeftEx, RightEx);
Expression main = Cond.Test;
Expression<Func<int, int, bool>> Lam = Expression.Lambda<Func<int, int, bool>>(main,
  new ParameterExpression[] { LeftEx, RightEx });
Console.WriteLine(Lam.Compile().Invoke(333, 1200));

With Cond I either get true/false but not the LeftEx or RightEx that Condition should return.

I couldn't find anything in the documentation.


6/16/2009 9:33:35 AM

Expert Answer

I think you just need:

Expression<Func<int, int, int>> Lam =
    Expression.Lambda<Func<int, int, int>>(Cond, // <=== HERE
        new ParameterExpression[] { LeftEx, RightEx });

edit - btw - var is your friend here:

    var p1 = Expression.Parameter(typeof(int), "p1");
    var p2 = Expression.Parameter(typeof(int), "p2");
    var body = Expression.Condition(Expression.GreaterThan(p1, p2), p1, p2);
    var lambda = Expression.Lambda<Func<int, int, int>>(body, p1, p2);
    var func = lambda.Compile();
6/16/2009 9:52:34 AM

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