[squeak-dev] implicit type coercion

Nicolas Cellier nicolas.cellier.aka.nice at gmail.com
Tue Apr 16 08:50:46 UTC 2019

Hi Chris,
putting messages in Object is never intelligent, at best hackish, and at
worse bad style (because of littering and of such un-controlled side
The purpose of my changes was to distinguish comparison from arithmetic:
- for performing arithmetic, exact + inexact lead to an inexact, so it's OK
to convert asFloat.
- for performing comparison exact < inexact, you must not convert to
inexact or you wll change the relation.

I don't remember what drove me to such high level in hierarchy, but I think
that I had to cope with many objects pretending to perform arithmetic
(Collection, String, ...).
Or were the original messages already at high level?
We should feel free to revisit anyway!

I don't like implicit conversions when there is no well established

The example from Tim was excellent: should 1+$1 be 2 or 50?
Why is it different from 1+'1'?
Should we convert Boolean asInteger for cross language (in)convenience?
Should we have true = '1' then?

For me, this is opening a can of worms: a principle of most astonishment.
All those wanting to follow the astonishment path should first lesson once
more to:

In the same vein, I hate the null pattern. nil is not false, #() and '' are
not false, because empty is not false, 'false' is not true either (though
not empty), etc...
These extensions are obscuring the intentions, are equivoque, and are
delaying bug finding when un-intentional.

For example, in Matlab relations < and > are defined on complex: you hardly
never gonna need that...
except maybe when sorting the eigenvalues of a matrix- and even in this
case, you don't want to always use the same ordering,
There is no natural ordering preserving a<b & (c<d) ==> (a+c)<(c+d), so why
choose one rather than the other?
The net result is that it is delaying bug finding when you have an
unexpected complex result, the program continues and does something, it's
just that you don't know exactly what, you lost control...

Le mar. 16 avr. 2019 à 03:41, Chris Muller <asqueaker at gmail.com> a écrit :

> Kudos Fabio for noticing the non-symmetry in type coercion between
> Strings and Characters.  I was doing a little more research and
> noticed we have all these adapt'ing methods on *Object* (!!).
> Object>>#adaptToFloat:andCompare:
> Object>>#adaptToFloat:andSend:
> Object>>#adaptToFraction:andCompare:
> Object>>#adaptToFraction:andSend:
> Object>>#adaptToInteger:andCompare:
> Object>>#adaptToInteger:andSend:
> Object>>#adaptToScaledDecimal:andCompare:
> Browse origin showed methods added in 2006 by Kernel-nice.398 (version
> notes below).  The explanation given there and in all three Mantis
> reports relates to coercions between Integers and Floats.
> So, it doesn't appear that these were intended to encourage automatic
> coercion of ANY object to the numbers domain for interoperation with
> numbers, but its presence on Object maybe was the common superclass
> for the implementation.
> I submitted an alternative version to the Inbox which proposes
> symmetry between Strings and Characters to be that they both require
> explicit coercion.
> Whether to do automatic coercion in the language feels like a weighty
> decision.  My gut is telling me its better to be conservative in doing
> auto coercing, but I'm sure Nicolas' and others' can better articulate
> an the most intelligent path forward.
>  - Chris
> _____________
> Name: Kernel-nice.398
> Author: nice
> Time: 13 February 2010, 4:31:00.389 am
> UUID: f1525362-d01a-214c-94fe-2bb3a5fffa89
> Ancestors: Kernel-nice.397
> Fix
> http://bugs.squeak.org/view.php?id=3360
> http://bugs.squeak.org/view.php?id=3374
> http://bugs.squeak.org/view.php?id=6601
> hash and = are now reconciled for numbers.
> = is now transitive for numbers.
> WARNING: now, tests like (1/10 = 0.1) will answer false.
> This is expected, and more than expected, this is wanted.
> Float are inexact and testing for strict equality is not a clever thing to
> do.
> All this has been longly debated at
> http://permalink.gmane.org/gmane.comp.lang.smalltalk.pharo.devel/10642
> http://thread.gmane.org/gmane.comp.lang.smalltalk.sapphire.devel/10223/focus=10228
> Please, read carefully this thread to make an opinion before raising your
> voice.
> It can break code eventually,  so I'm all ears to real case, and
> willing to help fixing. But please, real examples, not theoretical
> (after 8 month change in Pharo, I'm not aware of further complaints).
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