diff options
author | Xavier Noria <fxn@hashref.com> | 2009-09-12 13:25:06 +0200 |
---|---|---|
committer | Xavier Noria <fxn@hashref.com> | 2009-09-12 13:25:06 +0200 |
commit | 848bdaaa222603c9efefc7b7a22e35ddc25a0f0f (patch) | |
tree | 3fbf5e67bb8ba82f4f4d782cb75e89182c658b19 /railties/guides | |
parent | d74783e78e9620b1d7f6c2abefdcfee5b1261355 (diff) | |
download | rails-848bdaaa222603c9efefc7b7a22e35ddc25a0f0f.tar.gz rails-848bdaaa222603c9efefc7b7a22e35ddc25a0f0f.tar.bz2 rails-848bdaaa222603c9efefc7b7a22e35ddc25a0f0f.zip |
AS guide: documents Hash#diff
Diffstat (limited to 'railties/guides')
-rw-r--r-- | railties/guides/source/active_support_overview.textile | 36 |
1 files changed, 36 insertions, 0 deletions
diff --git a/railties/guides/source/active_support_overview.textile b/railties/guides/source/active_support_overview.textile index ce548f28d2..5723fbffa2 100644 --- a/railties/guides/source/active_support_overview.textile +++ b/railties/guides/source/active_support_overview.textile @@ -1130,6 +1130,42 @@ Active Support defines +Hash#deep_merge+. In a deep merge, if a key is found in The method +deep_merge!+ performs a deep merge in place. +h4. Diffing + +The method +diff+ returns a hash that represents a diff of the receiver and the argument with the following logic: + +* Pairs +key+, +value+ that exist in both hashes do not belong to the diff hash. + +* If both hashes have +key+, but with different values, the pair in the receiver wins. + +* The rest is just merged. + +<ruby> +{:a => 1}.diff(:a => 1) +# => {}, first rule + +{:a => 1}.diff(:a => 2) +# => {:a => 1}, second rule + +{:a => 1}.diff(:b => 2) +# => {:a => 1, :b => 2}, third rule + +{:a => 1, :b => 2, :c => 3}.diff(:b => 1, :c => 3, :d => 4) +# => {:a => 1, :b => 2, :d => 4}, all rules + +{}.diff({}) # => {} +{:a => 1}.diff({}) # => {:a => 1} +{}.diff(:a => 1) # => {:a => 1} +</ruby> + +An important property of this diff hash is that you can retrieve the original hash by applying +diff+ twice: + +<ruby> +hash1.diff(hash2).diff(hash2) == hash1 +</ruby> + +Diffing hashes may be useful for error messages related to expected option hashes for example. + h3. Extensions to +Range+ |