Each
suggest changeRuby has many types of enumerators but the first and most simple type of enumerator to start with is each
. We will print out even
or odd
for each number between 1
and 10
to show how each
works.
Basically there are two ways to pass so called blocks
. A block
is a piece of code being passed which will be executed by the method which is called. The each
method takes a block
which it calls for every element of the collection of objects it was called on.
There are two ways to pass a block to a method:
Method 1: Inline
(1..10).each { |i| puts i.even? ? 'even' : 'odd' }
This is a very compressed and ruby way to solve this. Let’s break this down piece by piece.
(1..10)
is a range from1
to10
inclusive. If we wanted it to be1
to10
exclusive, we would write(1...10)
..each
is an enumerator that enumerates overeach
element in the object it is acting on. In this case, it acts oneach
number in the range.{ |i| puts i.even? ? 'even' : 'odd' }
is the block for theeach
statement, which itself can be broken down further.
1. `|i|` this means that each element in the range is represented within the block by the identifier `i`. 2. `puts` is an output method in Ruby that has an automatic line break after each time it prints. (We can use `print` if we don't want the automatic line break) 3. `i.even?` checks if `i` is even. We could have also used `i % 2 == 0`; however, it is preferable to use built in methods. 4. ` ? "even" : "odd" ` this is ruby's ternary operator. The way a ternary operator is constructed is `expression ? a : b`. This is short for
ruby if expression a else b end
For code longer than one line the block
should be passed as a multiline block
. ## Method 2: Multiline
(1..10).each do |i|if i.even?puts 'even'elseputs 'odd'endend
In a multiline block
the do
replaces the opening bracket and end
replaces the closing bracket from the inline
style.
Ruby supports reverse_each as well. It will iterate the array backwards.
@arr = [1,2,3,4]
puts @arr.inspect # output is [1,2,3,4]
print "Reversed array elements["
@arr.reverse_each do |val|
print " #{val} " # output is 4 3 2 1
end
print "]\n"