metaprogramming - What is "for" in Ruby

Question

In Ruby:

for i in A do
    # some code
end

is the same as:

A.each do |i|
   # some code
end

for is not a kernel method:

• What exactly is "for" in ruby
• Is there a way to use other keywords to do similar things?

Something like:

 total = sum i in I {x[i]}

mapping to:

 total = I.sum {|i] x[i]}

Answer 1

It's almost syntax sugar. One difference is that, while for would use the scope of the code around it, each creates a separate scope within its block. Compare the following:

for i in (1..3)
  x = i
end
p x # => 3

versus

(1..3).each do |i|
  x = i
end
p x # => undefined local variable or method `x' for main:Object