Ruby garabage collector

[Ken Bloom]

In the "Why's poignant guide to Ruby" book, it states the following:

"If you can't get to an object through a variable, then Ruby will
figure you are done with it and will get rid of it. Periodically, Ruby
sends out its garbage collector to set these objects free."

The point I'm not getting here is: "If you can't get to an object
through a variable..."

Can you provide an examples that illustrates this?

Thanks.

a = [1,2,3].find {|x| x > 3}

puts a


In this (maybe too simple) example, x is garbage-collected once flow
leaves the block.

Nothing gets garbage collected here becuase 1,2, and 3 are value objects
(they're special in that they're not stored on the heap, but stored in
the memory that would be the pointer to most other objects), and because
they're still accessible through the array (a points to an array, which
points to each of the array's 3 elements) even after the loop ends.

A better example is:

irb(main):001:0> a=Object.new
=> #<Object:0x7f361c5dbe58>
irb(main):002:0> a=Object.new
=> #<Object:0x7f361c5d1c50>

at the end of this program, there is no longer a variable that points
(either directly or indirectly) to #<Object:0x7f361c5dbe58>, so it can be
garbage collected.

irb(main):003:0> a=[]
=> []
irb(main):004:0> b=Object.new
=> #<Object:0x7f361c5c33d0>
irb(main):005:0> a << b
=> [#<Object:0x7f361c5c33d0>]
irb(main):006:0> b=Object.new
=> #<Object:0x7f361c5a9890>
irb(main):007:0> a << b
=> [#<Object:0x7f361c5c33d0>, #<Object:0x7f361c5a9890>]
irb(main):008:0> b=Object.new
=> #<Object:0x7f361c5941c0>

In this example, nothing gets garbage collected. I allocated three
Objects, and one Array. At the end of execution, the Array is pointed to
by a, and two of the Objects are pointed to by the Array. The third
Object is pointed to by b.

 

[Bruno A]

I stand corrected. Thanks!

In the "Why's poignant guide to Ruby" book, it states the following:

"If you can't get to an object through a variable, then Ruby will
figure you are done with it and will get rid of it. Periodically, Ruby
sends out its garbage collector to set these objects free."

The point I'm not getting here is: "If you can't get to an object
through a variable..."

Can you provide an examples that illustrates this?

Thanks.

a = [1,2,3].find {|x| x > 3}

puts a


In this (maybe too simple) example, x is garbage-collected once flow
leaves the block.

Nothing gets garbage collected here becuase 1,2, and 3 are value objects
(they're special in that they're not stored on the heap, but stored in
the memory that would be the pointer to most other objects), and because
they're still accessible through the array (a points to an array, which
points to each of the array's 3 elements) even after the loop ends.

A better example is:

irb(main):001:0> a=Object.new
=> #<Object:0x7f361c5dbe58>
irb(main):002:0> a=Object.new
=> #<Object:0x7f361c5d1c50>

at the end of this program, there is no longer a variable that points
(either directly or indirectly) to #<Object:0x7f361c5dbe58>, so it can be
garbage collected.

irb(main):003:0> a=[]
=> []
irb(main):004:0> b=Object.new
=> #<Object:0x7f361c5c33d0>
irb(main):005:0> a << b
=> [#<Object:0x7f361c5c33d0>]
irb(main):006:0> b=Object.new
=> #<Object:0x7f361c5a9890>
irb(main):007:0> a << b
=> [#<Object:0x7f361c5c33d0>, #<Object:0x7f361c5a9890>]
irb(main):008:0> b=Object.new
=> #<Object:0x7f361c5941c0>

In this example, nothing gets garbage collected. I allocated three
Objects, and one Array. At the end of execution, the Array is pointed to
by a, and two of the Objects are pointed to by the Array. The third
Object is pointed to by b.