配列の全要素を指定した型にキャストしちゃうぞっていう拡張

ArrayExtension.cs

using System;
using System.Reflection;
using System.ComponentModel;
using System.Collections.Generic;

public static class ArrayExtension
{
    public static TOutput[] ConvertAll<TInput, TOutput>(this TInput[] self, TOutput defaultValue)
    {
        Type type = typeof(TOutput);
        TypeConverter converter = TypeDescriptor.GetConverter(type);
        MethodInfo parseMethod = type.GetMethod("Parse", new Type[] { typeof(string) });
        bool outputTypeIsString = defaultValue is string;

        return Array.ConvertAll(self, target => {
            TOutput result = defaultValue;
            try {
                if (parseMethod != null ) {
                    result = (TOutput)parseMethod.Invoke(null, new string[]{target.ToString()});
                } else if (outputTypeIsString || converter.CanConvertFrom(typeof(TInput))) {
                    result = (TOutput)converter.ConvertFrom(target.ToString());
                }
            } catch (Exception e) {
                // なにもしない
            }
            return result;
        });
    }
}