From: "Ara.T.Howard" <ahoward@...>
Date: 2004-03-09T23:34:42+09:00
Subject: Re: bizare yaml values

On Tue, 9 Mar 2004, Joel VanderWerf wrote:

> Ara.T.Howard wrote:
> > i have tk gui which owns a config object - derived from hash.  i have an
> > options menu configured with a callback that updates this has and another menu
> > that allows one to view this hash as a 'to_yaml' string.  after updating it
> > the values seem correct (inspect) and my code works properly, however the
> > to_yaml output shows bizarre values where it has been updated such as
> > 
> >   *id001
> >   &id001
> > 
> > the code in question is much to long to post, but i'm wondering what the
> > meaning of such values might mean and what type of situation might create
> > them.  i'm guessing it may have something to do with proc bindings and the
> > present value of a hash... but i'm pretty much at a loss at where to start
> > looking even...
> 
> No worries. It's just references:

ah - should have guessed - but i'm still worried!  ;-)

> irb(main):008:0> x = []
> => []
> irb(main):009:0> y = x
> => []
> irb(main):010:0> z = [x,y]
> => [[], []]
> irb(main):011:0> puts z.to_yaml
> ---
> - &id001 []
> - *id001
> => nil
> 
> Just for fun...
> 
> irb(main):012:0> x = []
> => []
> irb(main):013:0> x << x
> => [[...]]
> irb(main):014:0> puts x.to_yaml
> --- &id001
> - *id001
> => nil

that's plain enough.  but my situation is a bit different: i have a config
which is read in and YAML::load'd:

  ...
  ...
  gll:
    program              : gll_16_new
    rm_edge              : true
    limits              : [ 36, 68, 8, 97 ]
    direction            : ascending
    dem_path             : /dmsp/reference/srtm/
    ols_flag_definitions : /dmsp/reference/ref/ols_flags/OLS_flags.txt
    path                 : [ /dmsp/moby-1-1/zwdevel/dmspnl/ ]
    verbose              : true 
    use_middle_only      : true
  ...
  ...


and if i display THIS config (Hash) in a TkText using #to_yaml there are NO
references.  however, when i update limits from within the callback proc of a
tk button - something like:

  limits = [TkVariable.new, TkVariable.new, TkVariable.new, TkVariable.new]

  ul_lon = TkEntry.new w, :textvariable => limits[0]
  ul_lat = TkEntry.new w, :textvariable => limits[1]
  lr_lon = TkEntry.new w, :textvariable => limits[2]
  lr_lat = TkEntry.new w, :textvariable => limits[3]

  button = TkButton.new w

  button.configure :command => lambda {
    limits.map!{|limit| limit.to_s.to_f}
    @config['gll']['limits'] = limits
  }

and then re0display the config it appears as

  ...
  gll:
    ...
    limits: &id001
    ...
  ...

so, what i am asking is:  it was an array before, and it's an array after,
both arrays contain four floats (i can see this if i use pretty printing or
inspect instead of to_yaml to display the object) - so WHY does it display as
a _reference_ the second time?

-a
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