Props to Jeremy Voorhis for this cool and simple Hash maneuver.
class Hash def rewrite mapping inject({}) do |rewritten_hash, (original_key, value)| rewritten_hash[mapping.fetch(original_key, original_key)] = value rewritten_hash end end end
Example usage:
h = { :human => 'squishy', :robot => 'tinny' } h.rewrite(:human => :mammal) # => { :mammal => 'squishy', :robot => 'tinny' }
Interestingly, this is the first time I’ve seen argument decomposition used in a truly clear and helpful way.
That’s a beautiful method. Which part is the “argument decomposition” part? I Googled for “ruby argument decomposition” about all I get is this very post!
October 15th, 2008
A block passed to inject takes two arguments. The first is the accumulator, and the second is the element of the enumerable being injected (or folded.)
The decomposition in this case occurs in the second argument of the inject block, which instead of assigning the enumerable element to a single block-local variable, instead decomposes the Hash tuple (key, value) to two discrete locals. Neat!
October 15th, 2008
Oh yeah. For folks who want to find more of these in the wild, here’s a TextMate regexp that will find all injects that use argument decomposition:
inject.*[|][^|(\n]*[(][^)|\n]+[)][^|\n]*[|]
That makes sense when injecting on anything whose each method yields an array and Hash is a real common one (yielding [key,value]).
October 17th, 2008