ruby - Poking around in parent's internal state -

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tl:dr how decoupling work? need little example

i'm reading programming ruby - pragmatic programmer's guide. (http://ruby-doc.org/docs/programmingruby/html/tut_classes.html)

there example on how implement to_s subclass karaokesong of song.

class karaokesong < song # ... def to_s "ks: #{@name}--#{@artist} (#{@duration}) [#{@lyrics}]" end end asong = karaokesong.new("my way", "sinatra", 225, "and now, the...") asong.to_s    »  "ks: way--sinatra (225) [and now, the...]"

now bad way it:

say decided change song store duration in milliseconds. suddenly, karaokesong start reporting ridiculous values. idea of karaoke version of ``my way'' lasts 3750 minutes frightening consider.

instead should define to_s super:

def to_s super + " [#{@lyrics}]" end

now when @duration variable still stores song duration in miliseconds, how new to_s calls parent's method solve problem? still returns 3750 minutes, doesn't it?

i think dont understand difference between 2.

it's assumed song take care of proper output of @duration.

and if decide change song store duration in milliseconds, change song#to_s method , won't have change to_s of descendants.


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