Question about attr_accessor

[Roland Swingler]

Hi,

I came across something unexpected today, and wondered if anyone could
explain it to me. If I have this class:

class Foo
def initialize
@bar = 0
end

attr_accessor :bar

def add
bar += 1
end
end

then the "add" function doesn't work - it complains about a nil
object. You have to specifically put "self.bar += 1". Why is that - I
thought that the "self" was implicitly there?

Doing:

f = Foo.new
f.add

works as the class stands, so you only seem to need the self if you
are calling the accessor from within your class.

Confused...

TIA
Roland

 

[Martin Boese]

Change your add method to:

def add
@bar+=1
end

If you use just 'bar' it will think of a local variable which is not defined.

martin

 

[Robert Klemme]

Hi,

I came across something unexpected today, and wondered if anyone could
explain it to me. If I have this class:

class Foo
def initialize
@bar = 0
end

attr_accessor :bar

def add
bar += 1
end
end

then the "add" function doesn't work - it complains about a nil
object. You have to specifically put "self.bar += 1". Why is that - I
thought that the "self" was implicitly there?

bar += 1 is translated to "bar = bar + 1". When Ruby sees "bar =" it
takes bar to be a local variable. Hence you have to prefix with
"self.". See:
http://www.ruby-doc.org/docs/ProgrammingRuby/html/language.html#UO

Kind regards

robert

 

[Harry]

Hi,

I came across something unexpected today, and wondered if anyone could
explain it to me. If I have this class:

class Foo
def initialize
@bar = 0
end

attr_accessor :bar

def add
bar += 1
end
end

then the "add" function doesn't work - it complains about a nil
object. You have to specifically put "self.bar += 1". Why is that - I
thought that the "self" was implicitly there?

Doing:

f = Foo.new
f.add

works as the class stands, so you only seem to need the self if you
are calling the accessor from within your class.

Confused...

TIA
Roland

attr_accessor :bar refers to the instance variable @bar.
bar and @bar are not the same.


Harry

 

[dblack]

Hi --

Hi,

I came across something unexpected today, and wondered if anyone could
explain it to me. If I have this class:

class Foo
def initialize
@bar = 0
end

attr_accessor :bar

def add
bar += 1
end
end

then the "add" function doesn't work - it complains about a nil
object. You have to specifically put "self.bar += 1". Why is that - I
thought that the "self" was implicitly there?

For methods that end in = (like bar=), you always need an explicit
receiver, even if it's self, because otherwise Ruby will see it as an
assignment to a local variable.


David

--
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A. RUBY FOR RAILS by David A. Black (http://www.manning.com/black)
(See what readers are saying! http://www.rubypal.com/r4rrevs.pdf)
Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
A. Ruby Power and Light, LLC (http://www.rubypal.com)

 

[Roland Swingler]

Great - thanks for clearing that up.