# When use self.method\_name and when only method\_name?

**URL:** <https://www.ruby-forum.com/t/when-use-self-method-name-and-when-only-method-name/177087>\
**Category:** Ruby\
**Created:** [October 11, 2009, 11:16am UTC](https://www.ruby-forum.com/t/when-use-self-method-name-and-when-only-method-name/177087 "2009-10-11T11:16:06Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![josh](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/45deac/32.png) [@josh](https://www.ruby-forum.com/u/josh)\
**Post date:** [October 11, 2009, 11:16am UTC](https://www.ruby-forum.com/t/when-use-self-method-name-and-when-only-method-name/177087/1 "2009-10-11T11:16:06Z")

</div>

Hi all

Just a small newbie question: When calling a method inside an object, I  
should always use self.method\_name for good style, right? I know that I  
could always only use “method\_name”, but it’s a bit prone to errors  
because I could have also a local variable called “method\_name”, and  
when I use “self.” I always call the method, and not a potentially  
available local variable.

So it’s always better style to use:

def validate  
self.errors.add\_to\_base("…")  
end

instead of:

def validate  
errors.add\_to\_base("…")  
end

Right? 🙂

Thanks  
Josh

---

<div class="post-metadata">

**Author:** ![josh](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/45deac/32.png) [@josh](https://www.ruby-forum.com/u/josh)\
**Post date:** [October 11, 2009, 12:14pm UTC](https://www.ruby-forum.com/t/when-use-self-method-name-and-when-only-method-name/177087/2 "2009-10-11T12:14:06Z")

</div>

Hi –

On Sun, 11 Oct 2009, Joshua M. wrote:

> Right? 🙂  
> In general I prefer to leave off the optional “self.” except in a  
> couple of cases. The one that comes to mind mainly is:

def \<=\>(other)  
self.age \<=\> other.age  
end

where I like having the explicit receiver on both sides.

It’s definitely not unidiomatic to leave off the self. In fact, the  
whole private access level depends on it – and even if you’re not  
using a lot of private methods, that’s enough to confirm that it’s  
acceptable stylistically.

David

–  
The Ruby training with D. Black, G. Brown, J.McAnally  
Compleat Jan 22-23, 2010, Tampa, FL  
Rubyist [http://www.thecompleatrubyist.com](http://www.thecompleatrubyist.com)

David A. Black/Ruby Power and Light, LLC ([http://www.rubypal.com](http://www.rubypal.com))

---

<div class="post-metadata">

**Author:** ![josh](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/45deac/32.png) [@josh](https://www.ruby-forum.com/u/josh)\
**Post date:** [October 11, 2009, 12:20pm UTC](https://www.ruby-forum.com/t/when-use-self-method-name-and-when-only-method-name/177087/3 "2009-10-11T12:20:00Z")

</div>

David A. Black wrote:

> In fact, the  
> whole private access level depends on it

What do you mean with this exactly?

---

<div class="post-metadata">

**Author:** ![josh](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/45deac/32.png) [@josh](https://www.ruby-forum.com/u/josh)\
**Post date:** [October 13, 2009, 11:26am UTC](https://www.ruby-forum.com/t/when-use-self-method-name-and-when-only-method-name/177087/4 "2009-10-13T11:26:25Z")

</div>

Joshua M. wrote:

> Just a small newbie question: When calling a method inside an object, I  
> should always use self.method\_name for good style, right? I know that I  
> could always only use “method\_name”, but it’s a bit prone to errors  
> because I could have also a local variable called “method\_name”, and  
> when I use “self.” I always call the method, and not a potentially  
> available local variable.

It’s good style to keep methods small. Remember that every method starts  
with a clean sheet of local variables - they _never_ propagate in from  
outside - so it’s obvious by inspection whether a name is a local  
variable or not.

But there is a much larger class of errors such as simple typos:

```
self.method_nmae
slef.method_name

```

You’ll need unit tests to counter these; and once you have them, these  
will also cover other logic errors including the accidental shadowing of  
a method with a local variable as you describe above.

BTW, I still sometimes write  
foo = xxx

when I mean to call the method,  
self.foo = xxx

I suppose writing ‘self.’ everywhere would make that less likely - but  
I’d still say it’s better to have good unit tests.

---

<div class="post-metadata">

**Author:** ![josh](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/45deac/32.png) [@josh](https://www.ruby-forum.com/u/josh)\
**Post date:** [October 11, 2009, 12:34pm UTC](https://www.ruby-forum.com/t/when-use-self-method-name-and-when-only-method-name/177087/5 "2009-10-11T12:34:01Z")

</div>

Hi –

On Sun, 11 Oct 2009, Joshua M. wrote:

> David A. Black wrote:
> 
> > In fact, the  
> > whole private access level depends on it
> 
> What do you mean with this exactly?

A private method can only be called without an explicit receiver  
(except for =-terminated methods). For example:

class Baker  
def bake\_cake  
make\_batter # private method  
put\_in\_oven # private method  
puts “Cake is done!”  
end

```
 private
 def make_batter
   puts "Privately making the batter!"
 end

 def put_in_oven
   puts "Privately putting the cake in oven!"
 end

```

end

b = Baker.new  
b.bake\_cake

In this code, I can call the private methods only when I _don’t_ have  
an explicit receiver, including self. If I try to do this:

b.make\_batter

I get an error. Also, if I rewrite bake\_cake like this:

def bake\_cake  
self.make\_batter  
put\_in\_oven  
puts “Cake is done!”  
end

I get an error, because I’m calling make\_batter with an explicit  
receiver.

So Ruby uses the bareword style of method call to enforce privateness.  
The exception is the setter methods (like age=), which always require  
an explict receiver. In such cases, the receiver must be “self” (i.e.,  
exactly the word “self”, not a variable reference to self).

David

–  
The Ruby training with D. Black, G. Brown, J.McAnally  
Compleat Jan 22-23, 2010, Tampa, FL  
Rubyist [http://www.thecompleatrubyist.com](http://www.thecompleatrubyist.com)

David A. Black/Ruby Power and Light, LLC ([http://www.rubypal.com](http://www.rubypal.com))