如何声明具有匿名类型的字段（C＃）

Question

In the code below,how do I declare myLine as a public(global) variable? The problem is that I can't use the keyword "var".

    public static IEnumerable<string> ReadLines(StreamReader reader)
    {
        while (!reader.EndOfStream)
        {
            yield return reader.ReadLine();
        }
    }

    private void Filter1(string filename)
    {
        using(var writer = File.CreateText(Application.StartupPath + "\\temp\\test.txt"))
        {
            using (var reader = File.OpenText(filename))
            {
                int[] Ids = { 14652, 14653, 14654, 14655, 14656, 14657, 14658, 14659, 14660 };
                var myLine = from line in ReadLines(reader)
                             where line.Length > 1
                             let id = int.Parse(line.Split('\t')[1])
                             where Ids.Contains(id)
                             let m = Regex.Match(line, @"^\d+\t(\d+)\t.+?\t(item\\[^\t]+\.ddj)")
                             where m.Success == true
                             select new { Text = line, ItemId = id, Path = m.Groups[2].Value };


                foreach (var id in myLine)
                {
                    writer.WriteLine("Item Id = " + id.ItemId);
                    writer.WriteLine("Path = " + id.Path);
                    writer.WriteLine("\n");
                }

            }
        }
    }

I want to do it ,because I have to find a way to gain access to that ienumerable for later use.

Answer 1

The trouble is that it's using an anonymous type, which you can't use in a field declaration.

The fix is to write a named type with the same members, and use that type in your query. If you want it to have the same behaviour as your anonymous type, it should:

• Take all the values in the constructor
• Be immutable, exposing read-only properties
• Override Equals , GetHashCode and ToString
• Be sealed

You could just use Reflector to decompile the code, but then you'd end up with a generic type which you don't really need.

The class would look something like:

public sealed class Foo
{
    private readonly string text;
    private readonly int itemId;
    private readonly string path;

    public Foo(string text, int itemId, string path)
    {
        this.text = text;
        this.itemId = itemId;
        this.path = path;
    }

    public string Text
    {
        get { return text; }
    }

    public int ItemId
    {
        get { return itemId; }
    }

    public string Path
    {
        get { return path; }
    }

    public override bool Equals(object other)
    {
        Foo otherFoo = other as Foo;
        if (otherFoo == null)
        {
            return false;
        }
        return EqualityComparer<string>.Default.Equals(text, otherFoo.text) &&
        return EqualityComparer<int>.Default.Equals(itemId, otherFoo.itemId) &&
        return EqualityComparer<string>.Default.Equals(path, otherFoo.path);
    }

    public override string ToString()
    {
        return string.Format("{{ Text={0}, ItemId={1}, Path={2} }}",
                             text, itemId, path);
    }

    public override int GetHashCode()
    {
        int hash = 17;
        hash = hash * 23 + EqualityComparer<string>.Default.GetHashCode(text);
        hash = hash * 23 + EqualityComparer<int>.Default.GetHashCode(itemId);
        hash = hash * 23 + EqualityComparer<string>.Default.GetHashCode(path);
        return hash;
    }
}

Your query would just change at the end to:

select new Foo(line, id, m.Groups[2].Value)

Answer 2

Instead of using an anonymous class with the new keyboard, define a class explicitly with a Text, ItemId, etc. Then the type would be IQueryable<MyClass>. Use that instead of the var keyword.