Law of Demeter - is it really communicating only to friends?

Question

I read some article on Law of Demeter and it gets me confused.

It states that something like this:

var width = mapControl.get_mapState().getMapRange().getSize().get_width();

Should be replaced by this:

var mapState = mapControl.get_mapState();
var mapRange = mapState.get_mapRange();
var width = mapRange.get_width()

I am a little confused here cause the latter one is just the same as the first one but written differently. In both cases I am eventually accessing "width" which is not a direct friend of my current class.

So why is the second way really better?

it was printed stuff, otherwise there would be some critical comments immediately below. That's why it got me confused. — RobertPorter, Aug 19 '15 at 19:26

score 1 · Accepted Answer · edited Jun 20 '20 at 09:12

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I am a little confiused here cause the latter one is just the same as the first one but written differently. In both cases I am eventually accessing "width" which is not a direct friend of my current class.

So why is the second way really better?

It's not really better. A Law of Demeter approach would be to refactor the code, so the client code looks like this:

var width = mapControl.get_width();

In this case, client code doesn't need to know that mapControl has a "state", which has a "range", which has a "width". It just needs to know it exposes a "width".

edited Jun 20 '20 at 09:12

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answered Aug 31 '15 at 15:07

utnapistim

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That's how I understood it, I guess the source must have been not reliable and contained a misinterpretation. – RobertPorter Sep 30 '15 at 21:20

Law of Demeter - is it really communicating only to friends?

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