In Ruby, why does a method invocation not be able to be treated as a unit when "do" and "end" is use
- by Jian Lin
The following question is related to
http://stackoverflow.com/questions/2127836/ruby-print-inject-do-syntax
The question is, can we insist on using DO and END and make it work with puts or p?
This works:
a = [1,2,3,4]
b = a.inject do |sum, x|
sum + x
end
puts b # prints out 10
so, is it correct to say, inject is a class method of the Array class, which takes a block of code, and then returns a number. If so, then it should be no different from calling a function and getting back a return value:
b = foo(3)
puts b
or
b = circle.getRadius()
puts b
In the above two cases, we can directly say
puts foo(3)
puts circle.getRadius()
so, there is no way to make it work directly by using the following 2 ways:
a = [1,2,3,4]
puts a.inject do |sum, x|
sum + x
end
but it gives
ch01q2.rb:7:in `inject': no block given (LocalJumpError)
from ch01q2.rb:4:in `each'
from ch01q2.rb:4:in `inject'
from ch01q2.rb:4
grouping the method call using ( ) doesn't work either:
a = [1,2,3,4]
puts (a.inject do |sum, x|
sum + x
end)
and this gives:
ch01q3.rb:4: syntax error, unexpected kDO_BLOCK, expecting ')'
puts (a.inject do |sum, x|
^
ch01q3.rb:4: syntax error, unexpected '|', expecting '='
puts (a.inject do |sum, x|
^
ch01q3.rb:6: syntax error, unexpected kEND, expecting $end
end)
^
finally, the following version works:
a = [1,2,3,4]
puts a.inject { |sum, x|
sum + x
}
but why doesn't the grouping of the method invocation using ( ) work? What if a programmer insists that he uses do and end, can it be made to work directly with p or puts, without an extra temporary variable?
