Actions
Bug #16498
closedHash#transform_values in 2.7.0 sets new hash's default to old hash's default_proc
Status:
Closed
Assignee:
-
Target version:
-
ruby -v:
ruby 2.7.0p0 (2019-12-25 revision 647ee6f091) [x86_64-linux]
Description
The following is unexpected for me.
Hash.new { }.transform_values { }.default
# => #<Proc:0x000055eecda01510 -e:1>
Hash.new { }.transform_values { }[:any]
# => #<Proc:0x0000563a12e35510 -e:1>
Hash.new { :default }.transform_values { }[:any][]
# => :default
I did not think a default_proc
would turn into a default. The previous behaviour in 2.6 was that the default would be nil
, so this is new in 2.7. But I didn't see this mentioned in the 2.7 NEWS. May I learn of the proper use for this and/or whether it is intentional?
If you wonder when we might see something like this, I had found it with code similar in idea to the following:
weights = Hash.new { |h, k| h[k] = [] }
weights[:apple] << 1
weights[:apple] << 2
prices = weights.transform_values { :arbitrary }
puts (prices[:mango] || [])[0] || "We're all out of mangoes today"
in `block in <main>': undefined method `[]=' for 0:Integer (NoMethodError)
That was quite a confusing error message. It took a while to realise why []=
was called on 0
.
We also cannot fix this by using dig
(puts prices.dig(:mango, 0) || "We're all out of mangoes today"
) because then, we would get:
in `dig': Proc does not have #dig method (TypeError)
Actions
Like0
Like0Like0Like0Like0Like0Like0Like0Like0Like0Like0Like0