c# 全角と半角のカウント

shift-jisのサポートがない場合。

using System;
using han_zen;
class Program
{
    static void Main(string[] args)
    {
        //usage
        Console.WriteLine("あいうえを ".getWidth());
        Console.WriteLine("" + 'ｱ'.isHalfWidth());
        Console.WriteLine("" + 'ｱ'.getWidth());
        Console.WriteLine("" + '亜'.getWidth());

        Console.WriteLine("Hello World!");
    }
}//class

namespace han_zen
{
    using System.Text.RegularExpressions;
    using System.Linq;
    static class ZenkakuExtension
    {
        static Regex ptn = _();
        static Regex _()
        {
            var range = ""
            + "a-z"
            + "A-Z"
            + "0-9"
            + "!\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~ "
            + "ｱ-ﾞ" //半角カナ
            ;
            return new Regex($"^[{range}]+$");
        }
        public static bool isHalfWidth(this string @str) => ptn.IsMatch(@str);
        public static bool isFullWidth(this string @str) => !@str.isHalfWidth();
        public static bool isHalfWidth(this char @ch) => ("" + @ch).isHalfWidth();
        public static bool isFullWidth(this char @ch) => !@ch.isHalfWidth();
        public static int getWidth(this char @ch) => @ch.isHalfWidth() ? 1 : 2;
        public static int getWidth(this string @str) => @str.Select(getWidth).Sum();

    }//class

}//namespace