["H", "A", "L"].collect {|x| x.succ } # => ["I", "B", "M"] but
["H", "A", "L"].each {|x| x.succ } # => ["H", "A", "L"]
What is causing the difference in output here?
The succ method increments a string.
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The result of the block in Array#each are completely discarded, the result of each is the array itself (that's why you get the original ["H","A","L"]). Here you want a collect/map as you show in the first snippet (which creates a new array and leaves the old one untouched).
The output of each is discarded because each is the classical imperative for-loop: you need to do some kind of side-effect (read from a file, print to screen, update an array/hash, ...) to effectively do something.
My advice is to avoid each unless there is a good reason for it. I mean, it's ok to use each to write lines to a file, for example, but never to emulate a map, select, inject, or other FP abstractions.
tokland
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would you explain a little more, why is the output discarded with Enumerable#each? – lampShade Nov 03 '11 at 18:45
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That's the way it works. Use `each` when you're interested in the operation; use `collect` or its synonym `map` when you're interested in the output. Read the docs for more info. – Marnen Laibow-Koser Nov 03 '11 at 18:54
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An alternate approach using each_char:
"HAL".each_char.map {|x| x.succ } # => ["I", "B", "M"]
or just map
["H","A","L"].map {|x| x.succ } # => ["I", "B", "M"]
Cheers :)
Sean Vikoren
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nice one tokland...and that inspires this: "HAL".chars.map(&:succ).inject(""){|s,c| s << c} # => "IBM" – Sean Vikoren Nov 03 '11 at 21:37
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"HAL".chars.inject(""){|s,c| s << c.succ} for an inject bassed solution. – Sean Vikoren Nov 04 '11 at 18:21