----- Original Message ----- 
From: "Rob Stewart" <stewart@[...].com> 
To: <boost@[...].org> 
Cc: <boost@[...].org> 
Sent: Tuesday, May 18, 2004 9:42 AM
Subject: Re: [boost] Ranged type mini-library submission


[snip]
>  > I just changed the code by removing the public constraints typedef and
>  > adding a static function get_constraints() so that it can be invoked
using
>  > instances of an object as well.
>  >
>  > The problem with parameter inheritance, as least in this case, is that
it
>  > surprises programmers by causing an object to have an inconsistent
>  > interface. Most programmers when confronted with code such as
mytype::max()
>  > expect that max will be available for all instances of mytype. On the
other
>  > hand, mytype::get_constraints().max() is generally understood to not
always
>  > be readily available in a parameterized type.
> 
>  I don't understand mytype::get_constraints().max() to not always
>  be available.  If I wanted that information, I'd write that
>  expression (instead of mytype::max()) and then be surprised when
>  it didn't work.

When working with any parameterized type, it is natural to expect the return
value of some functions to be of a type equal to a parameter. It is not
natural to expect that the existance of methods to be conditional on the
parameter.

>  It's simple enough to require that the template parameter supply
>  min() and max() so that derivation yields those functions in
>  mytype's interface.  Then, it's a moot point whether min() and
>  max() are part of a static or non-static interface for mytype.

The constrained_value type allows constraints which have nothing to do with
min() and max() so requiring it in the parameter seems arbitrary.

>  > I don't see how the advantage of the shorthand justifies the case for
>  > parameter inheritance here.
> 
>  I don't see that you've solved any problem with your approach.

I am simply tryign to use parameterized types in a more manner that is more
widely understood and fits the natural assumptions of programmers.

Christopher Diggins
http://www.cdiggins.com
http://www.heron-language.com

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