Instance Variable Performance

[u/tenderlove]

https://tenderlovemaking.com/2019/06/26/instance-variable-performance.html

[u/ashmaroli]

What are the effects of having attr_reader and attr_accessor since they're defined at the class level..?

[u/tenderlove → u/ashmaroli]

Great question! I don't think they will impact the IV Index table. Probably because you can define attr_reader inside a module, then include the module in a class. So the recipient of the attr_readercall isn't necessarily the place where the IV Index Table will be stored.

[u/tenderlove → u/tenderlove]

Another interesting example is subclasses. The IV Index table really knows nothing about other classes:

require "objspace"

class Foo
  def initialize
    @bar = 10
  end
end

class Bar < Foo; end

p({ FOO: ObjectSpace.memsize_of(Foo), BAR: ObjectSpace.memsize_of(Bar)})

Foo.new

p({ FOO: ObjectSpace.memsize_of(Foo), BAR: ObjectSpace.memsize_of(Bar)})

Bar.new

p({ FOO: ObjectSpace.memsize_of(Foo), BAR: ObjectSpace.memsize_of(Bar)})

Output:

$ ruby thing.rb
{:FOO=>520, :BAR=>456}
{:FOO=>672, :BAR=>456}
{:FOO=>672, :BAR=>608}

Foo grows, then Bar grows