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From: Robert Klemme <shortcutter@googlemail.com>
Newsgroups: comp.lang.ruby
Subject: Re: reduce, map, :+ and :upcase as blocks and symbols as arguments
Date: Thu, 5 Jul 2018 08:23:33 +0200
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On 28.06.2018 11:25, Fernando Basso wrote:
> Why does `reduce' work passing both `&:+' _and_ `:+', but `map' seems to
> accept only `&:upcase' (but not `:upcase`)?
> 
>>> (1..5).reduce(:+)
> => 15
>>> (1..5).reduce(&:+)
> => 15
>>> ['x', 'y', 'z'].map(:upcase)
> ArgumentError: wrong number of arguments (given 1, expected 0)
> from (pry):3:in `map'
>>> ['x', 'y', 'z'].map(&:upcase)
> => ["X", "Y", "Z"]
> 
> Docs for `Enumerable#reduce' say:
> 
> ""
> Combines all elements of enum by applying a binary
> operation, specified by a block or a symbol that names a
> method or operator.
> ""
> 
> Docs `Enumerable#map' say:
> 
> ""
> Returns a new array with the results of running block once
> for every element in enum.
> ""
> 
> So, is that `reduce' takes both a block and a symbol, while map takes
> only a block?

Yes.

> And if so, is that some Ruby inconsistency?

Yes.

Actually I am surprised that #reduce / #inject accepts a single Symbol. 
But these methods have some subtleties in argument handling anyway, so 
maybe I should not be surprised.

Kind regards

	robert


-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/