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Diffstat (limited to 'guides/source')
| -rw-r--r-- | guides/source/active_support_core_extensions.textile | 32 |
1 files changed, 32 insertions, 0 deletions
diff --git a/guides/source/active_support_core_extensions.textile b/guides/source/active_support_core_extensions.textile index 80faffa49c..1f92d9d5f5 100644 --- a/guides/source/active_support_core_extensions.textile +++ b/guides/source/active_support_core_extensions.textile @@ -2549,6 +2549,38 @@ There's also the bang variant +except!+ that removes keys in the very receiver. NOTE: Defined in +active_support/core_ext/hash/except.rb+. +h5. +transform_keys+ and +transform_keys!+ + +The method +transform_keys+ accepts a block and returns a hash that has applied the block operations to each of the keys in the receiver: + +<ruby> +{nil => nil, 1 => 1, :a => :a}.transform_keys{ |key| key.to_s.upcase } +# => {"" => nil, "A" => :a, "1" => 1} +</ruby> + +The result in case of collision is undefined: + +<ruby> +{"a" => 1, :a => 2}.transform_keys{ |key| key.to_s.upcase } +# => {"A" => 2}, in my test, can't rely on this result though +</ruby> + +This method may be useful for example to build specialized conversions. For instance +stringify_keys+ and +symbolize_keys+ use +transform_keys+ to perform their key conversions: + +<ruby> +def stringify_keys + transform_keys{ |key| key.to_s } +end +... +def symbolize_keys + transform_keys{ |key| key.to_sym rescue key } +end +</ruby> + +There's also the bang variant +transform_keys!+ that applies the block operations to keys in the very receiver. + +NOTE: Defined in +active_support/core_ext/hash/keys.rb+. + h5. +stringify_keys+ and +stringify_keys!+ The method +stringify_keys+ returns a hash that has a stringified version of the keys in the receiver. It does so by sending +to_s+ to them: |