[squeak-dev] Collection>sum fails on empty collection

Nicolas Cellier nicolas.cellier.aka.nice at gmail.com
Tue Jan 8 21:54:14 UTC 2019

You can always write:

    ^collec inject: 0 into: #+

or whatever default zero you need:

   ^collec inject: 0 at 0 into: #+

Le mar. 8 janv. 2019 à 21:18, tim Rowledge <tim at rowledge.org> a écrit :

> > On 2019-01-08, at 12:10 PM, Eliot Miranda <eliot.miranda at gmail.com>
> wrote:
> >
> > IIRC we discussed this issue carefully.  The issue was typing.  Clearly
> one should only be able to compute the sum of a collection of numbers (or
> things that answer to + and can be an argument to 0 + ...).  So we wanted
> to check that there was at least one numbers element in the receiver and
> hence chose that sum should indeed fail for an empty collection.  It still
> seems like a reasonable choice to me.  see e.g.
> http://forum.world.st/squeak-dev-Re-Collection-gt-gt-sum-implementation-td77002.html#a77008
> I'm sure much thought was put into it; it's never easy trying to make
> really well crafted high-generality code. I certainly see the value for the
> #reduce: code as a general thing. I always did have a problem with messages
> like sum, average, median, and so on being implemented for general
> collections, for exactly the reason you point out - collections aren't all
> that often of purely numeric things.
> In the particular case I stumbled over, the usage of #sum carries way too
> many assumptions and provides no way to recover from them. Indeed the
> entire algorithm in that part of the code collapses with a big "oh bugger".
> tim
> --
> tim Rowledge; tim at rowledge.org; http://www.rowledge.org/tim
> Useful Latin Phrases:- Sentio aliquos togatos contra me conspirare = I
> think some people in togas are plotting against me.
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