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Re: Short Refactoring Tip: let the object do it for you

by dws (Chancellor)
on May 19, 2003 at 21:46 UTC ( #259310=note: print w/replies, xml ) Need Help??


in reply to Short Refactoring Tip: let the object do it for you

If we need to change those names, this code will be break pretty quickly.

Not only that, but forcing a client to write

if ($po->status->name eq 'Pending') { ...
requires them to know that a purchase order has a status, and that the status has a name. Both of those details are probably inappropriate for client code that deals with purchase orders to have to know. It also makes purchase orders harder to unit test, since you then have to either unit test a Status at the same time, or rig up mock objects to use in places of a Status. By structuring the API like
if ($po->can_send) { ...
you reduce the complexity of testing.

There's a design principle--whose name I'm blanking on (Demeter's Law -- thanks, lachoy)--that says that if you find yourself writing expressions that navigate more than one level into an object structure, the top-level object needs a different protocol. In the case above, can_send is that new protocol, and status can be made private (e.g., by renaming it to _status).

Replies are listed 'Best First'.
Re: Re: Short Refactoring Tip: let the object do it for you
by lachoy (Parson) on May 19, 2003 at 22:21 UTC

    That's the Law of Demeter, or at least part of it.

    Chris
    M-x auto-bs-mode

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[1nickt]: Corion HPs? ugh. I was impressed with Lenovo's gaming laptops; if it weren't for the red backlighting and general flashiness of the aesthetic, I might have gone with that. But all that was until I discovered that the Dell Precision line is still around.
[1nickt]: stevieb I don;t doubt that there's a difference. BestBuy has "consumer" models only on display.
[ambrus]: 1nickt: for some reason, these days they call every computer "gaming", even ones that gamers wouldn't buy. I've bought a keyboard that was labelled "gamer", despite that it has hard springs and seems to be way better for typing than for gaming;
[1nickt]: I though the gamers like that because they bash the keys so hard.
[ambrus]: and I've seen motherboards with no fast expansion ports for a video card but built-in hardware RAID advertized as "gaming".
LanX has a shaming laptop
[ambrus]: 1nickt: my impression is that the gamers like the softer springs, because fast reaction time is more important to them then feedback from keypresses to recognize typos.
[1nickt]: Ah, I see. I did read some gamer mag reviews, and yes, they lamented the fact that laptops with no discrete video card are sold as "gaming" hardware.
[1nickt]: But, they do have red keyboard backlighting! And gargoyles on the front, or words like "Maxxx" here and there. They know their demographic!
[1nickt]: True gamers don;t buy Dells, HPs, or Lenovos, I think ;-)

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