On 2/2/2015 11:16 AM, Steffen Märcker wrote:
> Hi,
>
> that's a more general question. Do you raise some sort of illegal
> argument exepction on a method call with improper arguments? If not,
> why not? If yes, do you throw a custom exception or some from the base
> library? It doesn't seem a too common practice in Smalltalk.
Typical practice is to *not* test argument type, the runtime system will
typically return an error 'soon enough'. Most often that will be a
MessageNotUnderstood exception, but that is not guaranteed...
What you do see is testing for certain argument values (as opposed to
types), one such use is in the base library to return a more precise
exception. For instance SequenceableCollection>>first will first check
the zero-th argument for emptyness before sending 'at: 1', which would
fail anyway on empty collections.
When your domain becomes complex I find it helpful to put such value
checks in more places using a 'self assert: [....] ' construct, thus
moving just slightly into the direction of contract based development.
To answer your 'why not' I guess that is a matter of pragmatics:
in stiffer typed environments like C, COM etc your app and associated
state will crash hard when the wrong type is passed in, in Smalltalk
your IDE would typically still be standing. So it is less of a problem
here (essentially bacause it is handled by the VM abstraction).
Reinout
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