DesignOnlyAttribute.cs

namespace System.ComponentModel
{
    [AttributeUsage(AttributeTargets.All)]
    public sealed class DesignOnlyAttribute : Attribute
    {
        private bool isDesignOnly;

        public static readonly DesignOnlyAttribute Yes = new DesignOnlyAttribute(isDesignOnly: true);

        public static readonly DesignOnlyAttribute No = new DesignOnlyAttribute(isDesignOnly: false);

        public static readonly DesignOnlyAttribute Default = No;

        public bool IsDesignOnly => isDesignOnly;

        public DesignOnlyAttribute(bool isDesignOnly)
        {
            this.isDesignOnly = isDesignOnly;
        }

        public override bool IsDefaultAttribute()
        {
            return IsDesignOnly == Default.IsDesignOnly;
        }

        public override bool Equals(object obj)
        {
            if (obj == this)
            {
                return true;
            }
            DesignOnlyAttribute designOnlyAttribute = obj as DesignOnlyAttribute;
            if (designOnlyAttribute != null)
            {
                return designOnlyAttribute.isDesignOnly == isDesignOnly;
            }
            return false;
        }

        public override int GetHashCode()
        {
            return isDesignOnly.GetHashCode();
        }
    }
}