chain

chain.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    public class MyEx1 : Exception
    {
        public MyEx1(string msg, Exception inner) : base(msg, inner) { }
    };

    public class MyEx2 : Exception
    {
    };

    public static class Chain
    {
        /// <summary>
        /// func()の結果を返す。例外が発生したらexc()が返す例外を投げる
        /// </summary>
        public static T begin<T>(Func<T> func, Func<Exception, Exception> exc)
        {
            try
            {
                return func();
            }
            catch (Exception ex)
            {
                throw exc(ex);
            }
        }

        /// <summary>
        /// func()の結果を返す。例外が発生したらexc()が返す例外を投げる
        /// </summary>
        public static TNext chain<T, TNext>(this T value, Func<T, TNext> func, Func<Exception, Exception> exc)
        {
            try
            {
                return func(value);
            }
            catch (Exception ex)
            {
                throw exc(ex);
            }
        }

        /// <summary>
        /// func()の結果を返す。
        /// </summary>
        public static TNext chain<T, TNext>(this T value, Func<T, TNext> func)
        {
            return func(value);
        }

        /// <summary>
        /// 値をチェックして、NGならexc()が返す例外を投げる。OKならその値をそのまま返す
        /// </summary>
        public static T assert<T>(this T value, Predicate<T> pred, Func<T, Exception> exc)
        {
            if (!pred(value))
                throw exc(value);
            else
                return value;
        }
    }

    class Program
    {
        static int ExecuteF()
        {
            return 1;
        }

        static string ExecuteG(int x)
        {
            return x.ToString();
        }

        static int ExecuteH(string x)
        {
            return int.Parse(x);
        }

        static void Main(string[] args)
        {
            // F, G, Hを順番に実行。F、Gで例外が出たらMyEx1を、Hの結果が0ならMyEx2を投げる
            var value = Chain.begin(ExecuteF,
                                    ex => new MyEx1("F failed", ex))
                             .chain(ExecuteG,
                                    ex => new MyEx1("G failed", ex))
                             .chain(ExecuteH)
                             .assert(x => x != 0,
                                     x => new MyEx2());
            Console.WriteLine(value);
            Console.Read();
        }
    }
}