[BUG?] #fetch does not provide a key attribute to the fallback block (but should provide)

[0exp]

ActiveSupport::Cache::Storage abstraction requires that #fetch/#fetch_multi methods provides a key to the block used for generating entries that does not exist in cache storage (with a given key).

I found that ActiveSupport::Cache::DalliStore#fetch missed this logic (in my own project).

This pull request resolves this.

now it works correctly:

# INCORRECT:
cache.fetch("a") { |key| "#{key}-calculated" } # in current implementation the key is nil
# => { "a" => "-calculated" }

# CORRECT (pull request)
cache.fetch("a") { |key| "#{key}-calculated" } # in current pull request the key has a corresponding value
# => { "a" => "a-calculated" }

[petergoldstein]

@0exp Can you please point me to the reference in the original abstraction? I'm not seeing this in the docs.

[0exp]

@petergoldstein sure:

#fetch_multi provides a cache key name (ActiveSupport::Cache::Store#fetch_multi):
https://github.com/rails/rails/blob/master/activesupport/lib/active_support/cache.rb#L439

#fetch provides a cache key name (ActiveSupport::Cache::Store#fetch):
https://github.com/rails/rails/blob/master/activesupport/lib/active_support/cache.rb#L331

---

This is really useful when you work with a set of keys (via #fetch_multi)

[petergoldstein]

@0exp Interesting. Definitely there in the code, but not at all reflected in the docs. All of their example blocks have no parameters.

Thanks for the contribution.