I'm writing code that evaluates .NET Expression
trees. I'm trying to create a C# 4 test to exercise my handling of an ExpressionType.Index
, but I can't figure out how to creat开发者_开发知识库e that type of expression through a LambdaExpression
. No matter what I try, the expression comes out as an ExpressionType.Call
or ExpressionType.ArrayIndex
. For example:
IList<int> myList = new ObservableCollection<int> { 3, 56, 8 };
Expression<Func<int>> myExpression = () => myList[3];
// myExpression.Body.NodeType == ExpressionType.Call
myList = new int[] { 3, 56, 8 };
myExpression = () => myList[3];
// myExpression.Body.NodeType == ExpressionType.Call
int[] myArray = new int[] { 3, 56, 8 };
myExpression = () => myArray[3];
// myExpression.Body.NodeType == ExpressionType.ArrayIndex
List<int> myNonInterfaceList = new List<int> { 3, 7, 4, 2 };
myExpression = () => myNonInterfaceList[3];
// myExpression.Body.NodeType == ExpressionType.Call
What is an IndexExpression
, and can one be created through an inline LambdaExpression
in C# 4?
An IndexExpression
is exactly what you expect (i.e., array access or indexer property). It's one of the many new expression types that was ported over from the DLR. The C# 4.0 compiler, however, uses the same expression types as its previous version, so it won't use IndexExpression
anywhere. Other languages may do so if their designers wish it.
To create an IndexExpression
programmatically, use the static ArrayAccess()
,MakeIndex()
, or Property()
methods on the Expression
class.
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