linq_functions

gistfile1.cs

public class LinqQuery<T>
{
    Action<Action<T>> _source;

    public LinqQuery(Action<Action<T>> source)
    {
        _source = source;
    }

    public LinqQuery(T[] array)
    {
        _source = (act) =>
                      {
                          for (var i = 0; i < array.Length; i++) act(array[i]);
                      };
    }

    public LinqQuery(IList<T> list)
    {
        _source = (act) =>
                      {
                          for (var i = 0; i < list.Count; i++) act(list[i]);
                      };
    }

    public LinqQuery<T> Where(Func<T, bool> f)
    {
        var pre = _source;
        _source = (act) => pre(item => { if (f(item)) act(item); });

        return this;
    }

    public LinqQuery<TR> Select<TR>(Func<T, TR> f)
    {
        return new LinqQuery<TR>(act => _source(item => act(f(item))));
    }

    public IList<T> ToList()
    {
        var list = new List<T>();
        _source(list.Add);
        return list;
    }
}

public static class Linq
{
    public static LinqQuery<T> Where<T>(this IList<T> list, Func<T, bool> f)
    {
        return new LinqQuery<T>(list).Where(f);
    }

    public static LinqQuery<TR> Select<T,TR>(this IList<T> list, Func<T,TR> f)
    {
        return new LinqQuery<T>(list).Select(f);
    }
}

// test
// var list = new List<int>{1,2,3,4}
// list.Where(i=>i%2==0).Select(i*i).ToList(); // 4,16