This post originated from an RSS feed registered with .NET Buzz by Jeff Key. Original Post: To ReadOnly or not to ReadOnly? Feed Title: Jeff Key Feed URL: http://www.asp.net/err404.htm?aspxerrorpath=/jkey/Rss.aspx Feed Description: Topics revolve around .NET and the Windows platform. Latest .NET Buzz Posts Latest .NET Buzz Posts by Jeff Key Latest Posts From Jeff Key

BradA occasionally posts API design questions on his blog and the flood of comments never disappoint.  Yesterday's question was regarding read-only collections:  Should a potentially read-only collection be derived from a read-only class, or should it have a ReadOnly property that indicates whether it's read-only. 

I think it depends whether it's a class whose context is within an application versus a library.  If it a class in an application, then the latter is fine.  The behavior is known and expected.  However, if it's in a library such as the FCL, I prefer the latter.  Imagine if there was a read-only flag on ArrayList or Hashtable.  Before adding/removing any members you'd always have to check it's ReadOnly property.  Completely unnecessary.  If it extended a ReadOnlyArrayList, then there is no question what it supports.  If you need read-only, you type your param/variable/whatever as ReadOnlyArrayList; if you need to write to it, you type it as ArrayList. 

Regardless, it's worth a read.  Everyone has valid comments.