What are methods ending in =?

rubyonrails-talk
1

Greg Christopher wrote:

Hi,

I was wondering what methods ending in an equal sign meant, but am not sure what to search for? Could anyone point me to any resources or tell me some terms to search for.

Thanks!

-Greg

It's sugar syntax!

So the method assign=(user_id), can be written in ruby: @object.assign = user_id

Note the spaces around the equal sign :slight_smile:

2

Got it - maybe. I found a good resource[1], but I am not sure I understand the value of the setter method in the first place. It would seem that benefit is being able to skip explicitly calling save on an object. Is that right?

The benefit of getter and setter methods are many - essentially they allow you to perform operations on the variable before and after they are retrieved or set. This is part of object-oriented methodology. But in reference to your first question - "I was wondering what methods ending in an equal sign meant", it is a feature of Ruby itself that methods can end in "!", "?" and "=", and the community has taken these to mean "potentially dangerous/exception creating", "interrogative (should return a boolean)" and "sets a variable", respectively.

If I had this method defined on my class:

def my_attribute=(some_value) @some_value = some_value end

I could call:

@object.my_attribute = new_value

instead of:

@object.my_attribute = new_value @object.save

Is that the reason to define a setter method?

No, because in #my_attribute=, you did not call save. Here is a reason to define a setter method:

class Shape   def save_intersection=(shape)     @intersection = self.calculate_intersection(shape)   end end

That is, we need to calculate the intersection of these two shapes and then we can store the result in an instance variable. This is a good use of the setter syntax, because it sets a variable, and we need to do something "special". However, if we're not doing anything special with the variable being set, it is preferable to write:

class Shape   attr_accessor :points end

Which automatically defines the methods #points, which gets the instance variable @points, and #points=, which will set the instance variable if you used it like:

shape = Shape.new shape.points = [1.2, 3,3]

Colin

3

Er, I mean, if that was you also. I forgot to check the original poster's name. :smiley:

Colin

4

Yeah, i was using my buddy's computer.

So, I think I understand, but want to make sure I understand how I would use these practically. Basically, using these ruby shortcuts allows me to better work with and manage variables that I won't immediately be saving with my object.

For instance, in your special case, if I need to calculate the intersection of two shapes for the view, but didn't need to save that value in my DB, then I would use the setter method?

Maybe in your second example, where I'm doing nothing special, but had these points, I'd be using those points in a view or some other output, but wouldn't be returning them to be stored on a record, at least not immediately. Yes?

Thanks!

-Greg