HashMagic simply contains a couple of spin-off data structures based on the basic Ruby Hash:
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SlashedHash
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OrderedHash
You can use either of those separately or in combination. Note that ruby-1.9 Hashes are made to keep their order, but I’m not sure about setting an order explicitly for them, and definitely not setting an order ahead of time.
SlashedHash
The concept of a SlashedHash is to flatten down a multi-level Hash structure into a single-level Hash whose keys represent the pathway to the data in the original multi-level structure. For example,
>> sh = {'a' => 'b', 'c' => {'d' => :e, 'f' => ['a', 'b']}, 'd' => ['e', 'f']}.slashed
=> {slashed: "a"=>"b", "c/d"=>:e, "d"=>["e", "f"], "c/f"=>["a", "b"]}
Once you transform a Hash into a SlashedHash, the only negative differences are:
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All but the end-point (or ‘leaf node’) data are turned into strings. Restated: Any data at the “end” of a Hash multi-level structure is left alone, but all keys in between, whether string, symbol, or anything else, is turned into a string in order to pack them together into a “slashed” key.
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Speed. A Ruby Hash is built into the core and written mostly in C so it is very fast; but a SlashedHash clones the same C functionality on all the Hash’s methods so that it can act as a normal Hash but with more sugar.
Like I said, the above mentioned things are the only negative differences. You can still access items by their original keys – to continue the example above,
>> sh['c']['d']
=> :e
BUT you can also access the same values by their “slashed” keys:
>> sh['c/d']
=> :e
>> sh['c/f']
=> ["a", "b"]
And you can access the keys either normally or flattened:
>> sh.keys
=> ["a", "c", "d"]
>> sh.flat.keys
=> ["a", "c/d", "d", "c/f"]
Accessing one level into the SlashedHash gives you another SlashedHash, if applicable:
>> sh['c']
=> {slashed: "d"=>:e, "f"=>["a", "b"]}
What good is SlashedHash? What can it do for me?
1) It comes in VERY handy when doing special transformations or multi-level key mappings. Think of reading an XML structure into specific property names (example uses the formattedstring gem syntax):
>> joe = "<person><name>Joe Schmoe</name><age>25</age><parent><name>Joseph Schmoe</name><age>56</age></parent>".formatted(:xml).to_hash.slashed
=> {slashed: "person"=>{"name"=>"Joe Schmoe", "age"=>"25", "parent"=>{"name"=>"Joseph Schmoe", "age"=>"56"}}}
>> mapping = {'name' => 'person/name', 'age' => 'person/age', 'parent_name' => 'person/parent/name', 'parent_age' => 'person/parent/age'}
>> joe.transform_keys_with_mapping(mapping)
=> {"name"=>"Joe Schmoe", "parent_name"=>"Joseph Schmoe", "age"=>"25", "parent_age"=>"56"}
2) It is useful for sorting multi-level hashes by integration with OrderedHash.
/ / / Still writing, will come back to this sometime... :) / / /