Feature #6684
Object#do
Status:
Rejected
Priority:
Normal
Assignee:
-
Target version:
-
Description
=begin
#Object#do
This is my first post.
初めての投稿です。よろしくお願いします。
Let me propose a new method Object#do.
次のような実装のObject#doを提案します。
class Object
def do(*args, &blk)
yield(self, *args)
end
end
do encapsulate a sequencial procedure into a block. It makes some temporal variables to be block local and enhance code readability. I might say that do is an Object#tap with block result, or is Array#map for one item.
doはオブジェクトに対する一連の処理をブロック内に閉じ込めます。それによって、一時変数のブロック内への局所化、コードの可読性向上を実現します。結果を返すObject#tap、単項版Array#mapと見ることができます。
##Usage
# calculate average and standard deviation for list
#
# without `do`
scores = [56, 87, 49, 75, 90, 63, 65]
scores.inject(:+) / scores.size # => 69
avg = scores.inject(:+) / scores.size
sigmas = scores.map { |n| (avg - n)**2 }
sd = Math.sqrt(sigmas.inject(:+) / scores.size) # => 14.247806848775006
# with `do`
avg = [56, 87, 49, 75, 90, 63, 65].do { |s| s.inject(:+) / s.size } # => 69
sd = scores.do { |s|
avg = s.inject(:+) / s.size
sigmas = s.map { |n| (avg - n)**2 }
Math.sqrt(sigmas.inject(:+) / s.size)
}
sd # => 14.247806848775006
# create a hash from a set of lists
#
# without `do`
h = Hash[ [:a, :b, :c].zip([1, 2, 3]) ] # => {:a=>1, :b=>2, :c=>3}
# with `do`
h = [:a, :b, :c].zip([1,2,3]).do { |arr| Hash[arr] } # => {:a=>1, :b=>2, :c=>3}
# sum of array using recursion
#
# without `do`
def sum(lst, mem=0)
return mem if lst.empty?
sum(lst.drop(1), mem+lst.first)
end
sum [*1..5], 5 # => 20
# or
def sum(lst, mem=0)
return mem if lst.empty?
fst, *tail = lst
sum(tail, mem+fst)
end
# with `do`
def sum(lst, mem=0)
return mem if lst.empty?
lst.do { |fst, *tail| sum(tail, mem+fst) }
end
sum2 [*1..5], 5 # => 20
BasicObject#instance_eval works for the above, but it not appropriate for them.
同様の目的はBasicObject#instance_evalでも実現できますが、この種の一般的演算には適さないと考えます。
Thank you for your consideration.
=end
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