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Mastering Expression Trees With .NET Reflector

4.60/5 (4 votes)
5 Aug 2010CPOL 15K  
Following my last post, I received lots of enquiries about how to master the creation of expression trees.

Following my last post, I received lots of enquiries about how to master the creation of expression trees.

The answer is .NET Reflector.

In that post, I needed to generate an expression tree for this expression:

C#
Expression<Func<object, object>> expression = o => ((object)((SomeType)o).Property1);

I just compiled that code in Visual Studio 2010, loaded the assembly in .NET Reflector, and disassembled it to C# without optimizations (View –> Options –> Disassembler –> Optimization: None).

The disassembled code looked like this:

C#
Expression<Func<object, object>> expression;
ParameterExpression CS$0$0000;
ParameterExpression[] CS$0$0001;
expression = Expression.Lambda<Func<object, object>>
	(Expression.Convert(Expression.Property(Expression.Convert
	(CS$0$0000 = Expression.Parameter(typeof(object), "o"), 
	typeof(SomeType)), (MethodInfo) methodof(SomeType.get_Property1)), 
	typeof(object)), new ParameterExpression[] { CS$0$0000 });

After giving valid C# names to the variables and tidying up the code a bit, I came up with this:

C#
ParameterExpression parameter = Expression.Parameter(typeof(object), "o");
Expression<Func<object, object>> expression =
    Expression.Lambda<Func<object, object>>(
        Expression.Convert(
            Expression.Property(
                Expression.Convert(
                    parameter,
                    typeof(SomeType)
                ),
                "Property1"
            ),
            typeof(object)
        ),
        parameter
    );

Easy! Isn’t it?

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)