Hi Martin,
 
Thanks. Your remark about setValidity makes sense. One question about try() though. Isn't that a (crude) implementation of duck typing? Give a method some type of data, 'try' if it works with that type of data, and if not, do something else? I think I agree with you that if-then is less of a "let's see what happens" kind of statement.

Cheers!!
Albert-Jan

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In the face of ambiguity, refuse the temptation to guess.
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--- On Mon, 3/8/10, Martin Morgan <mtmorgan@fhcrc.org> wrote:


From: Martin Morgan <mtmorgan@fhcrc.org>
Subject: Re: [R] setClass or setValidity?
To: "Albert-Jan Roskam" <fomcl@yahoo.com>
Cc: r-help@r-project.org
Date: Monday, March 8, 2010, 10:56 PM


On 03/08/2010 07:18 AM, Albert-Jan Roskam wrote:
> Sorry: there was an error in the last sentence:
> And, inside those validity checks, is most of the checking done with 'if' 'else' computations, or is it also common to use try()?

For me it's a matter of taste, and usual to use if... (because you know
explicitly what you're trying to validate, whereas try() implies a kind
of 'something might go wrong...'). I find myself using setValidity() to
separate out class definition from implementation.

Best,

Martin

> 
> Cheers!!
> Albert-Jan
> 
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> In the face of ambiguity, refuse the temptation to guess.
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> --- On Mon, 3/8/10, Albert-Jan Roskam <fomcl@yahoo.com> wrote:
> 
> 
> From: Albert-Jan Roskam <fomcl@yahoo.com>
> Subject: [R] setClass or setValidity?
> To: r-help@r-project.org
> Date: Monday, March 8, 2010, 4:14 PM
> 
> 
> Hi, 
>  
> I'm reading up on S4 classes *). There seem to be at least two ways of input validation:
> setClass() (using the 'validity' argument)  and setValidity(). Is it a matter of taste which function is used? Or should more complex validation code better be put in a setValiditity call?
> 
> *) A (Not So) Short Introduction to S4 Object Oriented Programming in R 
> V0.5.1 Christophe Genolini August 20, 2008
>  
> And, inside those validity checks, is most of the checking done with 'if' 'else' computations, or is it also common to use except()?
> 
> Cheers!!
> Albert-Jan
> 
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> In the face of ambiguity, refuse the temptation to guess.
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> 
>       
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> ______________________________________________
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-- 
Martin Morgan
Computational Biology / Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N.
PO Box 19024 Seattle, WA 98109

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