From simon.urbanek at r-project.org  Mon Jun 27 14:27:41 2011
From: simon.urbanek at r-project.org (Simon Urbanek)
Date: Mon, 27 Jun 2011 08:27:41 -0400
Subject: [Rd] Class not found when search in .onLoad
In-Reply-To: <4E082E83.3060204@cbio.uct.ac.za>
References: <4E0321DE.2020601@cbio.uct.ac.za> <4E036D6E.3000509@r-project.org>
	<4E044276.1070002@cbio.uct.ac.za> <4E04EDB1.70105@r-project.org>
	<4E082E83.3060204@cbio.uct.ac.za>
Message-ID: <A0A00B86-D685-443A-9CF2-AFBA7F260940@r-project.org>

On Jun 27, 2011, at 3:17 AM, Renaud Gaujoux wrote:

> 
> On 24/06/2011 22:04, John Chambers wrote:
>> 
>> Strictly speaking, that is not meaningful.  A class (like any R object) is uniquely referenced by a name *and an environment*.  The name of a package can be used to construct the environment, but your "character slot" won't identify a class reliably unless the character string has a "package" attribute.
>> 
>> Look at class(x), for example, from an object from one of these classes.  It will have a "package" attribute identifying the package.
>> The character string with the package attribute is what you should be storing in the slot (or else store the class definition---takes more space but is slightly more efficient).
>> 
> 
> Thank you for this clarification, I will make my factory method for the relevant class add the package attribute to the slot.
> Storing the class would require recreating the object if the user makes changes in the class definition. These objects are meant to be used when developing new algorithms. In this context one expects the user to do multiple tries and modifications, and I want to ease the process, by using dynamic links to classes (a character slot) rather than static links (result of getClass).
> 
> However, this does not explain why .onLoad does not find the class while .onAttach finds it, does it?
> Is .onLoad evaluated outside the namespace environment, while .onAttach is evaluated within the namespace?
> 

Look at the default of where - it is the top environment, not the evaluated one, and in .onLoad the namespace is not attached yet while it is in .onAttach.

Cheers,
S

Possibly @John: it's a bit puzzling that isClass has a default for where yet it is entirely ignored as getClassDef is called without where. If anyone changes the default in getDeffClass() then isClass signature will be misleading - is there a practical reason for this construct? Thanks, S.


[Rd] Class not found when search in .onLoad
Simon Urbanek