Question

I extend Dynamic.cs to qualify it for usage with indexers. In this scenario I need to get the index, which is stored in a call expression. In the debugger, I can see:

 -      left    {Param_0.get_Item(0)}   System.Linq.Expressions.Expression {System.Linq.Expressions.InstanceMethodCallExpressionN}
    -   Arguments   Count = 1   System.Collections.ObjectModel.ReadOnlyCollection<System.Linq.Expressions.Expression> {System.Runtime.CompilerServices.TrueReadOnlyCollection<System.Linq.Expressions.Expression>}
        -   [0] {0} System.Linq.Expressions.Expression {System.Linq.Expressions.ConstantExpression}
            CanReduce   false   bool
            DebugView   "0" string
            NodeType    Constant    System.Linq.Expressions.ExpressionType
            + Type  {Name = "Int32" FullName = "System.Int32"}  System.Type {System.RuntimeType}
            Value   0   object {int}
    +   Rohdatenansicht     

What I want is:

left.Arguments[0].Value

How can I get this?

An ugly method will be perhaps to use left.ToString(). This will result in: “Param_0.get_Item(0)” There I can extract the parameter of get_Item(). But I think this is not the right way.

Answer 1

To get to that value, you just need to cast the expressions to the right types:

Expression left = …

var methodCall = (MethodCallExpression)left;

var constant = (ConstantExpression)methodCall.Arguments[0];

int value = (int)constant.Value;

Alternatively, you can use dynamic:

dynamic dynamicLeft = left;

int value = dynamicLeft.Arguments[0].Value;