About Smalltalk at: .... ifAbsent:/present:
andreas.raab at gmx.de
Mon Nov 29 21:27:18 UTC 2004
Hi Stef -
> It seems that:
> - first it would be better to let the compiler compiles method with
> reference to classes that are not in the system and let the system
> complain at execution tim (marcus suggestion and he can explain that much
> better than me).
I doubt this. Yes, all of these could be re-written as, say:
Foo ifNil:[self mumble].
Foo ifNotNil:[Foo bar].
Smalltalk at: #Foo ifAbsent:[self mumble]
Smalltalk at: #Foo ifPresent:[:foo| foo bar].
but the main point is that the latter two are very verbose in conveying the
intention that "yes, the caller is very well aware that Foo may be absent
and that the dependency is a weak one". If you know how to read to the first
one the same may be true but the latter is just simply obvious in this
> - second, it occurred to us that packages are missing in some cases
> because having a dependency mechanism
> (I'm not sure that it is the solution) would make sure that the code
> needing to be invoked is present in the image by the structural dependency
> between packages or registration where optional code can be declared
I don't understand that. The whole point of using "Smalltalk at: #Foo
ifAbsent:" is to declare a weak dependency, e.g., the presence of Foo may
be advantageous but is by no means required. Of course, a dependency system
could model these weak dependencies as well but only at the cost of clarity
> We would really appreciate to get you open a browser, look at the code
> (clean if you identify some dead code, ugly methods ;)) and share with us
> your impressions. And what are the solutions you see, because it seems to
> us that there are far too much use of this idiom.
I'm not at all convinced that this is a bad idiom. The only problem I have
with it is that it doesn't come up when you browse the references to a class
(but that problem is easily fixable if someone just cares enough) and while
you have made some points on how to "fix" the idiom you haven't made a very
good (or bad ;-) argument why to fix it to begin with, e.g., why you'd think
this idiom is problematic.
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