C# 4.0 Implicitly Typed Dynamic Objects

Question

Data File: (Data.txt) lines represent width height

5
6 9
7 2
4 4

C# Code:

var list = new List<dynamic>();
using (var sr = new StreamReader("Data.txt", Encoding.UTF8))
{
    list = sr.ReadToEnd().Split('\n').Select(r =>
    {
        var split = r.Split(' ');
        var len = split.Length;
        return new {
            w = len > 0 ? int.Parse(split[0].Trim()) : 0,
            h = len > 1 ? int.Parse(split[1].Trim()) : 0 
        } as dynamic;
    }).ToList();
}
int Area = list.Sum(r => r.h * r.w);

The example works as is. I had to do a few undesired things to make it work.

First I had to declare the list to avoid the using scope - since I do not have a typed dimension object I made the type dynamic (var list = new List<dynamic>()).

The undesirable part is casting the anonymous object to a dynamic (as dynamic). Otherwise I get

Cannot implicitly convert type System.Collections.Generic.List<AnonymousType#1> to System.Collections.Generic.List<dynamic>

Why do I get this error? I know a dynamic can hold an anonymous type, so is this a problem with the ToList() extension and dynamics?

I need to be able to access the anonymous list items outside of the using statement, as in the last line that calculates area.

---

Solution: I went with dtb's answer. It avoided the use of a using statement and dynamics all together. Thank you all for the input!

var list = 
    (from line in File.ReadLines("Data.txt")
    let parts = line.Split(' ')
    let width = int.Parse(parts[0])
    let height = parts.Length > 1 ? int.Parse(parts[1]) : 0
    select new { width, height }).ToList();

Answer 1

You can use File.ReadLines to avoid the StreamReader.

IEnumerable<dynamic> query =
    from line in File.ReadLines("Data.txt")
    let parts = line.Split(' ')
    let width = int.Parse(parts[0])
    let height = parts.Length > 1 ? int.Parse(parts[1]) : 0
    select new { width, height } as dynamic;

List<dynamic> list = query.ToList();

int area = list.Sum(t => t.width * t.height);

However, as others have pointed out, using dynamic isn't really appropriate here. If you're using the query only within a method, an anonymous instance is good enough. If you want to use the result of the query outside the method, create a small struct or class or use Tuple<T1,T2>.