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Reducing the knowledge of internal structures is what the Law of Demeter (http://en.wikipedia.org/wiki/Law_of_Demeter http://en.wikipedia.org/wiki/Law_of_Demete

Reducing the knowledge of internal structures is what the Law of Demeter (http://en.wikipedia.org/wiki/Law_of_Demeter http://en.wikipedia.org/wiki/Law_of_Demeter) is about. Usually good practice.

steveklabnik 12y ago
DHH has repeatedly asserted that he thinks the Law of Demeter is bad, so that wouldn't work as a justification, at least in response to him.
- protomyth 12y ago
  What is his reasoning on it being bad?
  - pacala 12y ago
    There is (immutable) data and there are modules. Encapsulation / Demeter make it hard to work with data. OTOH, Encapsulation / Demeter are good for modules.
  - steveklabnik 12y ago
    I don't want to misrepresent him, so I'll just point you to these links: - http://signalvnoise.com/posts/3112-how-basecamp-next-got-to-be-so-damn-fast-without-using-much-client-side-ui#comment_72496 http://signalvnoise.com/posts/3112-how-basecamp-next-got-to-... - http://rubyrogues.com/056-rr-david-heinemeier-hansson/ http://rubyrogues.com/056-rr-david-heinemeier-hansson/ - https://www.youtube.com/watch?v=9LfmrkyP81M https://www.youtube.com/watch?v=9LfmrkyP81M
  - fxn 12y ago
    He does not say it is bad per se. What he criticizes is using any of these "laws" and "principles" as if they were truths, as if the argument was based on an axiom or had the strength of science. They are "inferred" from experience statistically speaking, but in each individual case you need to gauge and check yourself whether those three dots make or not make sense. It is your judgement in particular code that matters, not the a priori invocation of any "law" or "principle".
    - gary_bernhardt 12y ago
      DHH quote: "I think the Law of Demeter is shit and never follow it." (from http://signalvnoise.com/posts/3112-how-basecamp-next-got-to-be-so-damn-fast-without-using-much-client-side-ui#comment_72496 http://signalvnoise.com/posts/3112-how-basecamp-next-got-to-...)
      - fxn 12y ago
        Because he judges a series of dots by themselves, not because any law mandantes anything. He gives a shit about these grandiose names, show me the code and let's discus on that.
        gary_bernhardt 12y ago
        I was responding to your claim that "He does not say it is bad per se." Calling it "shit" seems like "[saying] it is bad".
        fxn 12y ago
        If you present a code with ten dots, he will probably say it is bad code. But he won't invoke law of demeter. That's the point I think. Is like invoking SRP. Fuck that. When you are experienced, you develop a sense on delineating responsabilities in a way that fits your application. I am not David of course, but I have participated in some discussions with him, and we think very much alike on these topics, I think what I say above is right. Going to switch to myself now: When people invoke SRP a priori they sometimes end up with one class == one method in a theoretical a priori way. I don't think that works. It goes in the reverse direction. SRP is inferred, it emerges, it is not applied as if it was a logical proposition.
        derefr 12y ago
        > When people invoke SRP a priori they sometimes end up with one class == one method in a theoretical a priori way. That's... not really what SRP means. This (http://blog.8thlight.com/uncle-bob/2014/05/08/SingleReponsibilityPrinciple.html http://blog.8thlight.com/uncle-bob/2014/05/08/SingleReponsib...) was on HN just a bit ago--Mr. Martin being the guy who gave us the term. Let me quote the essential bit: > And this gets to the crux of the Single Responsibility Principle. This principle is about people. > When you write a software module, you want to make sure that when changes are requested, those changes can only originate from a single person, or rather, a single tightly coupled group of people representing a single narrowly defined business function. You want to isolate your modules from the complexities of the organization as a whole, and design your systems such that each module is responsible (responds to) the needs of just that one business function.
- jrochkind1 12y ago
  Ah, but I think OP is a pretty good explanation of _why_ the Law of Demeter is actually good, although it doesn't use that phrase. I've been somewhat suspicious of the law of demeter (not firmly on one side or the other), but this article actually helped me see the value of it. It's not that "you can't do this because it violates the law of demeter." That's a ridiculous cargo cult way to use software design principles (which, yeah, is quite common). Rather, it's, the law of demeter is good because it prevents THIS stuff, which you don't want. Like, okay, DHH thinks the law of demeter is useless, but he hates things that... the law of demeter is meant to and helps prevent.
  - steveklabnik 12y ago
    I agree with you that the post is a great explanation of why Demeter is good. All I mean to say is "this is just Demeter" is not a refutation of "I think the Law of Demeter is shit and never follow it." (See my links in your sibling, that's a quote.)
- jimbokun 12y ago
  Citing dhh's opinion is not a justification for ignoring the law of Demeter, either, so what's your point?

Reducing the knowledge of internal structures is what the Law of Demeter (http://en.wikipedia.org/wiki/Law_of_Demeter http://en.wikipedia.org/wiki/Law_of_Demeter) is about. Usually good practice.

steveklabnik 12y ago

DHH has repeatedly asserted that he thinks the Law of Demeter is bad, so that wouldn't work as a justification, at least in response to him.

protomyth 12y ago
What is his reasoning on it being bad?
- pacala 12y ago
  There is (immutable) data and there are modules. Encapsulation / Demeter make it hard to work with data. OTOH, Encapsulation / Demeter are good for modules.
- steveklabnik 12y ago
  I don't want to misrepresent him, so I'll just point you to these links: - http://signalvnoise.com/posts/3112-how-basecamp-next-got-to-be-so-damn-fast-without-using-much-client-side-ui#comment_72496 http://signalvnoise.com/posts/3112-how-basecamp-next-got-to-... - http://rubyrogues.com/056-rr-david-heinemeier-hansson/ http://rubyrogues.com/056-rr-david-heinemeier-hansson/ - https://www.youtube.com/watch?v=9LfmrkyP81M https://www.youtube.com/watch?v=9LfmrkyP81M
- fxn 12y ago
  He does not say it is bad per se. What he criticizes is using any of these "laws" and "principles" as if they were truths, as if the argument was based on an axiom or had the strength of science. They are "inferred" from experience statistically speaking, but in each individual case you need to gauge and check yourself whether those three dots make or not make sense. It is your judgement in particular code that matters, not the a priori invocation of any "law" or "principle".
  - gary_bernhardt 12y ago
    DHH quote: "I think the Law of Demeter is shit and never follow it." (from http://signalvnoise.com/posts/3112-how-basecamp-next-got-to-be-so-damn-fast-without-using-much-client-side-ui#comment_72496 http://signalvnoise.com/posts/3112-how-basecamp-next-got-to-...)
    - fxn 12y ago
      Because he judges a series of dots by themselves, not because any law mandantes anything. He gives a shit about these grandiose names, show me the code and let's discus on that.
      - gary_bernhardt 12y ago
        I was responding to your claim that "He does not say it is bad per se." Calling it "shit" seems like "[saying] it is bad".
        fxn 12y ago
        If you present a code with ten dots, he will probably say it is bad code. But he won't invoke law of demeter. That's the point I think. Is like invoking SRP. Fuck that. When you are experienced, you develop a sense on delineating responsabilities in a way that fits your application. I am not David of course, but I have participated in some discussions with him, and we think very much alike on these topics, I think what I say above is right. Going to switch to myself now: When people invoke SRP a priori they sometimes end up with one class == one method in a theoretical a priori way. I don't think that works. It goes in the reverse direction. SRP is inferred, it emerges, it is not applied as if it was a logical proposition.
        derefr 12y ago
        > When people invoke SRP a priori they sometimes end up with one class == one method in a theoretical a priori way. That's... not really what SRP means. This (http://blog.8thlight.com/uncle-bob/2014/05/08/SingleReponsibilityPrinciple.html http://blog.8thlight.com/uncle-bob/2014/05/08/SingleReponsib...) was on HN just a bit ago--Mr. Martin being the guy who gave us the term. Let me quote the essential bit: > And this gets to the crux of the Single Responsibility Principle. This principle is about people. > When you write a software module, you want to make sure that when changes are requested, those changes can only originate from a single person, or rather, a single tightly coupled group of people representing a single narrowly defined business function. You want to isolate your modules from the complexities of the organization as a whole, and design your systems such that each module is responsible (responds to) the needs of just that one business function.
jrochkind1 12y ago
Ah, but I think OP is a pretty good explanation of _why_ the Law of Demeter is actually good, although it doesn't use that phrase. I've been somewhat suspicious of the law of demeter (not firmly on one side or the other), but this article actually helped me see the value of it. It's not that "you can't do this because it violates the law of demeter." That's a ridiculous cargo cult way to use software design principles (which, yeah, is quite common). Rather, it's, the law of demeter is good because it prevents THIS stuff, which you don't want. Like, okay, DHH thinks the law of demeter is useless, but he hates things that... the law of demeter is meant to and helps prevent.
- steveklabnik 12y ago
  I agree with you that the post is a great explanation of why Demeter is good. All I mean to say is "this is just Demeter" is not a refutation of "I think the Law of Demeter is shit and never follow it." (See my links in your sibling, that's a quote.)
jimbokun 12y ago
Citing dhh's opinion is not a justification for ignoring the law of Demeter, either, so what's your point?