I have in my program a number of parameters that can be set by the user, which I store in a hash %par. Now the thing is, some of these parameters come in more and less specific versions.

An example: We have a parameter "margin-left". In some cases, the user hasn't set a specific value for it; it then defers to the more general "margin-horizontal". If the user hasn't set a specific value for that, it in turn defers to the more general "margin".

In my current program, those "unspecified" parameters are set to "a" (for "automatic"). So when the time comes to actually draw the left margin, the program does something like

if($par{'margin-left'} ne 'a'){
  $actual = $par{'margin-left'}
}elsif($par{'margin-horizontal'} ne 'a'){
  $actual = $par{'margin-horizontal'}
}
else{$actual = $par{'margin'}}

[download]

As you can see, it's a bit of a bunch every time I just need to read the margin-left value. I could of course pack all that into a "get" sub, that would save on typing, but it still seems like a slow and clumsy method.

There is a "set" sub, so in principle I could use that to track and update everything, checking whenever a parameter is set whether it has any parent / dependant parameters, but that's also quite a lot of code, and it's redundant for all the parameters that don't have any such behaviour.

Is there a better way? Maybe something with referencing / aliasing? Ideally keeping all the inner working in the "set" sub, so I can just use $par{'margin-left'} and get the right thing.

In reply to Deferring variables by Chuma

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