How can I increment an Integer variable by X without creating a new object instance?
+= does not work because:
ree-1.8.7-2010.02 > x = 1
1
ree-1.8.7-2010.02 > x.object_id
3
ree-1.8.7-2010.02 > x += 1
2
ree-1.8.7-2010.02 > x.object_id
5
-
Are you asking out of curiosity, or is there a use case for this (such as concurrent programming)?Andrew Grimm– Andrew Grimm2010-11-23 22:36:32 +00:00Commented Nov 23, 2010 at 22:36
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5 Answers
You can't. Not in Ruby, and not in any other programming language I am aware of.
The object which represents the mathematical number 1 will always have the value 1. Mutating the object which represents the mathematical number 1 to suddenly have the value 2 would quite simply be insane, because now all of a sudden 1 + 1 == 4.
2 Comments
the Tin Man
And what's wrong with
1 + 1 == 4? They do it in government and corporations all the time! :-)
user3467349
You can mutate this in Python and I would guess also in Ruby - also this answer completely fails to address why this is the case. Consider the difference
a=12; b=12; b.object_id; a.object_id; vs (x = 9**57; y= 9**57; y.object_id; x.object_id)Extend your example for a moment. Try this:
x = 2
y = 1 + 1
x.object_id
y.object_id
Every unique number will have its own identity. Ruby's object orientedness goes a bit deeper than you will find with C++ and Java (both of those have the concept of primitives and classes).
What's important is that when you query x the second time for its value the value will be what you expect. Object identifiers don't really matter unless you are the garbage collector.
2 Comments
Andrew Grimm
In YARV ruby,
x and y both have object_ids of 5. Are they different to each other in your implementation?
Berin Loritsch
That was the point. The value 2 will have the same instance id, regardless of how you got there. In the end, object ids mean nothing--it's the variable you care about.
It gets worse with Bignums
begin
a = 1234567890
puts a.object_id
b = 1234567890
puts b.object_id
end
gave me
10605136
10604960
Comments
Execution time is really terrible even if just you organize a simple loop. Primitives shouldn't be ditched from Ruby.
(1..16000).each do
(1..16000).each do
end
end
This itself takes 30-40 seconds to complete (Lenovo T400, Virtualboxed Ubuntu), and you haven't even done something sophisticated.
Comments
You can use a helper class:
class Variable
def initialize value = nil
@value = value
end
attr_accessor :value
def method_missing *args, &blk
@value.send(*args, &blk)
end
def to_s
@value.to_s
end
# here's the increment/decrement part
def inc x = 1
@value += x
end
def dec x = 1
@value -= x
end
end
x = Variable.new 1
puts x #=> 1
puts x.object_id #=> 22456116 (or whatever)
x.inc
puts x #=> 2
puts x.object_id #=> 22456116
x.inc 3
puts x #=> 5
puts x.object_id #=> 22456116
More uses of "class Variable" here.
