From: Daniel Baird <danielbaird@...>
Date: 2006-03-15T16:17:52+09:00
Subject: Re: Hash default -- what's going on here?

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I'm guessing it's got something to do with your assignment

                        table[a]=3Dt

the array that is the hash's default can be assigned to.  I think that's
what you're doing.  If i did some testing I might be more sure :)

;Daniel

On 15/03/06, Pete Goodeve <pete@jwgibbs.cchem.berkeley.edu> wrote:
>
>
> I've hit what is either an egregious bug in ruby (1.8.4) or some subtlety
> that I haven't grasped.  [Most likely the latter... (:-)]
>
> Briefly I had two arrays of symbol strings of which I wanted to find
> which symbols occurred in both arrays, so I thought I'd use a hash with
> the key being the symbol and the value a two element array that would
> be used to flag which set(s) the symbol was found in.  The following
> is a simplified (and 'instrumented') version of what I was trying to
> do:
>
> listA=3D["line1","line2","line3"]
> listB=3D["line5","line3","line4"]
> table=3D{}
> table.default=3D[0,0]
> print "table default originally: ", table.default, "\n"
>
> listA.each {|a| t=3Dtable[a]; print a," -- undef value: ",t;
>                         t[0]=3D1; print "  new value: ",t,"\n";
>                         table[a]=3Dt}
> print "table default now: ", table.default, "\n"
>
> listB.each {|a| t=3Dtable[a]; print a," -- undef value: ",t;
>                         t[1]=3D1; print "  new value: ",t,"\n";
>                         table[a]=3Dt}
>
> print "table default now: ", table.default, "\ntable contents:\n"
> table.each {|k,v| print k, ": ", v[0], v[1], "\n"}
>
>
> Now, in the 'each' statements, the variable 'a' should (except in one
> case)
> not be in the hash yet, so I would expect the original provided default t=
o
> be returned.  However, here's the printout I get:
>
> table default now: 00
> line1 -- undef value: 00  new value: 10
> line2 -- undef value: 10  new value: 10
> line3 -- undef value: 10  new value: 10
> table default now: 10
> line5 -- undef value: 10  new value: 11
> line3 -- undef value: 11  new value: 11
> line4 -- undef value: 11  new value: 11
> table default now: 11
> table contents:
> line1: 11
> line2: 11
> line3: 11
> line4: 11
> line5: 11
>
>
> Dunhh?  Why is the default value getting changed?  I can't see that
> I'm resetting it anywhere.  If I do the same sort of manipulations
> outside of a block (one at a time in irb for instance) things happen
> as I would expect -- the default remains as set, and is returned for
> any undefined key.
>
> Illumination appreciated.
>                                 -- Pete --
>
>
>


--
Daniel Baird
http://danielbaird.com (TiddlyW;nks! :: Whiteboard Koala :: Blog :: Things
That Suck)
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