Question

puts [1,2,3].map do |x| 
  x + 1 
end.inspect

With ruby 1.9.2 this returns

<Enumerator:0x0000010086be50>

ruby 1.8.7:

# 1
# 2
# 3

assigning a variable…

x = [1,2,3].map do |x| 
  x + 1 
end.inspect

puts x

[2, 3, 4]

Moustache blocks work as expected:

puts [1,2,3].map { |x| x + 1 }.inspect

[2, 3, 4]

Answer 1

puts [1,2,3].map do |x| 
  x + 1 
end.inspect

Is parsed as:

puts([1,2,3].map) do |x| 
  x + 1 
end.inspect

I.e. map is called without a block (which will make it return the unchanged array in 1.8 and an enumerator in 1.9) and the block is passed to puts (which will just ignore it).

The reason that it works with {} instead of do end is that {} has different precedence so it’s parsed as:

puts([1,2,3].map { |x| x + 1 }.inspect)

Similarly the version using a variable works because in that case there is simply no ambiguity.