For the following Lambda expression:
GetPropertyNameAndArrayIndex(() => SomeArray[0])
I know that you can get the property name for an expression. I also know that you can get the array index by using a ConstantExpression and accessing the Right value. My question is how do you get array index (or Right value) when it is not a constant, I.E.,
for (int i = 0; i < 5; i++)
{
GetPropertyNameAndArrayIndex(() => SomeArray[i])
}
Any help would be greatly appreciated.
As already noted in comments; note that the example given is susceptible to issues with captured variables if used asynchronously - but probably OK "as is".
To do it thoroughly involves a lot of edge-cases (or you can cheat and use Compile()) - but here's an example that shows the overall themes (without using Compile):
using System;
using System.Linq.Expressions;
using System.Reflection;
class Program
{
static void Main()
{
string[] arr = { "abc", "def" };
for (int i = 0; i < arr.Length; i++)
{
Foo(() => arr[i]);
}
}
static object Foo<T>(Expression<Func<T>> lambda)
{
object obj = Walk(lambda.Body);
Console.WriteLine("Value is: " + obj);
return obj;
}
static object Walk(Expression expr)
{
switch (expr.NodeType)
{
case ExpressionType.ArrayIndex:
BinaryExpression be = (BinaryExpression)expr;
Array arr = (Array)Walk(be.Left);
int index = (int) Walk(be.Right);
Console.WriteLine("Index is: " + index);
return arr.GetValue(index);
case ExpressionType.MemberAccess:
MemberExpression me = (MemberExpression)expr;
switch (me.Member.MemberType)
{
case MemberTypes.Property:
return ((PropertyInfo)me.Member).GetValue(Walk(me.Expression), null);
case MemberTypes.Field:
return ((FieldInfo)me.Member).GetValue(Walk(me.Expression));
default:
throw new NotSupportedException();
}
case ExpressionType.Constant:
return ((ConstantExpression) expr).Value;
default:
throw new NotSupportedException();
}
}
}
