How to get MemberInfo of ArrayLength type expressions?

Question

Some trouble with UnaryExpressions.

This works this way:

Expression<Func<List<string>, object>> k = l => l.Count;
//got member in this case like this
var member = ((k.Body as UnaryExpression).Operand as MemberExpression).Member;

In the above case the k.Body.NodeType was ExpressionType.Convert. But it's a little tricky with ExpressionType.ArrayLength. How would I get the PropertyInfo member similarly in the below case?:

Expression<Func<string[], int>> k = l => l.Length;
var member = ??

In the second case k.Body is something like ArrayLength(l).

I can do it with a hack like this:

var member = (k.Body as UnaryExpression).Operand.Type.GetProperty("Length");

but this doesn't feel like a straight forward expression approach. It's more a plain old reflection call with dirty string "Length" passed. Is there a better way?

Redmond

Answer 1

It's an ArrayLength node, which you can create with the Expression.ArrayLength method.

It's just a UnaryExpression with an Operand which is the array expression, and a NodeType of ArrayLength. It's not entirely clear to me what you wanted to know about it, but hopefully the call to Expression.ArrayLength is what you were after.

EDIT: Although there is an Array.Length property, that's not what's used normally. For example:

int[] x = new int[10];
Array y = x;

int a = x.Length;
int b = y.Length;

... then evaluating x.Length uses the ldlen IL instruction whereas evaluating y.Length uses a call to the property.

Tetralogy

I want to know how to get the PropertyInfo of Length property from l.Length part of the expression. How do I get that from Expression.ArrayLength method? – Redmond

@nawfal: It's not a property, so there is no such PropertyInfo. – Tetralogy

I guess it is a property. For instance I can get the PropertyInfo of a typical int[].Length like typeof(int[]).GetProperty("Length"). – Redmond

@nawfal: Sorry, to clarify - that's the Array.Property length, but if you use int[] x = ...; int y = x.Length; then that doesn't use the property. – Tetralogy

Then what does it use ultimately? If anything shouldn't it have a MemberInfo associated with it? – Redmond

@nawfal: No, it's special basically. See my edit for more details. – Tetralogy