attr_accessor with default block
It's quite common to define attributes (like attr_reader, attr_accessor) with default values. It would be useful if Ruby provided a helper method for this case. attr_accessor and attr_reader can support this nicely using a default block:
# (1) Simple approach
@name ||= 'Hello'
# (2) nil-safe approach
return @name if defined? @name
@name = 'Hello'
# (3) This proposal
attr_accessor :name do
p = Person.new
p.instance_variable_get(:@name) # => nil
p.name # => 'Hello'
p.instance_variable_get(:@name) # => 'Hello'
Problems with current approaches:
- The reader and the writer looks widely different
- Solution 1 doesn't work as intended when the default value may evaulate to nil/false
- Solution 2 requires you to write the attribute name five times
#2 [ruby-core:56043] Updated by Magnus Holm over 2 years ago
On Mon, Jul 15, 2013 at 6:07 PM, rkh (Konstantin Haase) firstname.lastname@example.org wrote:
Issue #8635 has been updated by rkh (Konstantin Haase).
If this should be added, could you consider adding it with a
What do you mean?
Is it for thread-safety? In that case: I disagree. Concurrent classes needs
to be specifically designed, and I don't want to add any overhead to
Or is it for detecting recursive calls in the same thread?
#3 [ruby-core:56046] Updated by Avdi Grimm over 2 years ago
Just adding some prior art...
There have been many, many takes on this in various gems, but I thought I'd drop in a note about https://github.com/ahoward/fattr, which is my personal favorite and a gem I've used happily for many years. It might provide some implementation inspiration.