Replacing anonymous methods with expression tree

Question

If I want to replace this anonymous method:

Func<int, int> f = delegate(int i)
{
     return i + 1;
};

with an expression tree, it would like this:

ParameterExpression i = Expression.Parameter(typeof(int), "i");
Expression one = Expression.Constant(1, typeof(int));
Expression body = Expression.Add(i, one);
Func<int, int> f = Expression.Lambda<Func<int, int>>(body, i).Compile();

(I know: an expression tree will secretly dynamically create another anymous method, but that is not the point).

Now I want to replace the following method with an expression tree:

Func<int, int> f = delegate(int i)
{
     Debug.WriteLine("Inside the function!");
     return i + 1;
};

Is there a way and how do I do this?

score 1 · Accepted Answer · answered Apr 30 '13 at 10:16

Yes, you can do the replacement. The structure of your current expression looks like this:

Expression.Lambda
    Expression.Add
        Expression.Parameter("a")
        Expression.Constant(1)

the structure of the new expression will look like this:

Expression.Lambda
    Expression.BlockExpression
        Expression.Call
            Expression.Constant("Inside the function!")
            MedhodInfo(Debug.WriteLine)
        Expression.Add
            Expression.Parameter("a")
            Expression.Constant(1)

You will need to provide MedhodInfo for the Debug.WriteLine to the Call expression. The last expression in the block (i.e. a+1) will be considered block's return expression.

Replacing anonymous methods with expression tree

1 Answers1