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Rails
1

Im not familiar on dependency injection

Remove Car’s explicit reference to Engine by using dependency injection.

class Car
attr_reader :engine

def engine
@engine ||= Engine.new(4)
end

def move
engine.accelerate
end
end

class Engine
attr_reader :cylinders

def initialize(cylinders)
@cylinders = cylinders
end

def accelerate

end
end

2

On Monday, 12 May 2014 02:09:26 UTC-4, Joener Preagola wrote:

Im not familiar on dependency injection

Remove Car’s explicit reference to Engine by using dependency injection.

Posting homework / exercise questions verbatim is generally frowned upon
on
most mailing lists. A better start might be “here’s what I’ve tried, and
here’s what’s going wrong”, or “here’s what I’ve found in research but
it
doesn’t make sense”.

In this specific case, you may want to consider other ways that Car
could
get an Engine object besides constructing it explicitly in Car#engine.
Maybe pass it in as an argument, or change the attr_reader to an
attr_accessor and directly write it? Also consider splitting the “how”
(the
class to be constructed) from the “what” (the parameters passed to the
constructor).

–Matt J.

3

Joener Preagola wrote in post #1145843:

Im not familiar on dependency injection

Remove Car’s explicit reference to Engine by using dependency injection.

The first question to ask yourself is, “Why is it important to use
dependency injection in this specific scenario?”

After all this is Ruby, not some lame statically typed language like
Java or something. In Java Dependency Injection (DI) is uses to solve a
lots of issues that are mostly due to limitations of the language
itself. In fact it requires looking outside of the language itself to
even support DI (i.e. XML configuration files or Java annotations).

There’s a tendency to make DI sound like something magical or
complicated in the Java world, but in Ruby (and other dynamically typed
languages) you won’t here much about it. Mostly because it’s a really
simple concept with a really simple implementation.