I'm not sure what the original author was thinking of, but you can always
do this to perform validation:
TUPLE: my-model < model ;
: <my-model> ( value -- model ) my-model new-model ;
M: my-model value<<
over even? [ drop throw ] unless call-next-method ;
Then if you try and construct it with an odd number or set it with an odd
number value it throws.
On Tue, Jun 13, 2017 at 2:24 PM, Alexander Ilin <ajs...@yandex.ru> wrote:
> Hello!
>
> I have found this text in the documentation: "Models can override
> requests to change their value, for example to perform validation:
> set-model ( value model -- )".
>
> How would that work, exactly? `set-model` is not a generic that could be
> overridden. I don't understand the mechanism suggested by the help.
>
> For example, I'm developing a gadget for a certain type of objects, and
> I want only that class of objects to be assignable to the gadget's model
> slot. How would I do that kind of validation?
>
> Or is it not what I need in my case?
>
> ---=====---
> Александр
>
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