3. Ruby blocks:
○ Block consists of a chunk of code
○ We assign a name to block
○ Code inside a block is always enclosed within {} braces or do-
end.
○ A block can always be invoked from a function with same name
as the block. E.g. a block has name ‘check’ then it can be
invoked from a method named ‘check’.
○ We can invoke a block with using ‘yield’ statement.
○ We can pass parameters to block as well.
○ Real-time examples of block are array collect, select, map
within which can simply attach a block of code and process that
code on array, times loop i.e. 5.times do |a| …end.
4. #example1
def test
puts “we are in method”
yield
puts “we are in method”
yield
End
Test { puts “we are in block”}
>>> result will be :
You are in the method
You are in the block
You are again back to the method
You are in the block
#example2
10.times {|a| puts a }
5. Block, Proc, Lambda & methods:
○ Blocks, procs and lamdba are one of the most powerful aspects of ruby,
and also one of the most misunderstood too.
○ This can be because ruby handles CLOSURES in a bit different/unique
way. To make it more difficult its has four different ways of handling
closures.
○ Block: most common, easiest and arguably most “ruby like” way to use
closures in ruby.
○ Procedures AKA Procs: blocks are good, but we cant reuse them,
whenever we need we have to rewrite them. There comes Procs. Procs
are nothing more than a block that can be reused.
○ Lambda: lambda is almost similar to Procs except two subtle
differences,
○ unlike Procs, lambdas check the number of arguments passed and returns
error if not.
○ lambdas have diminutive returns.
○ Method: when we already have some method and want to pass it to
another method as a closure, we use ‘method’ method provided by ruby
to keep things DRY.
6. How Proc works?
class Array
def iterate!(code)
self.each_with_index do |n, i|
self[i] = code.call(n)
end
end
end
array_1 = [1, 2, 3, 4]
array_2 = [2, 3, 4, 5] #example2
def callbacks(procs) procs[:
square = Proc.new do |n|
starting].call
n ** 2 puts "Still going" procs[:
end finishing].call
array_1.iterate!(square) end
array_2.iterate!(square)
callbacks(:starting => Proc.new { puts
"Starting" }, :finishing => Proc.new {
puts "Finishing" })
7. Lambda: an example, how its different from Proc:
#example1
def args(code)
one, two = 1, 2
code.call(one, two)
end
args(Proc.new{|a, b, c|
puts "Give me a #{a} and a #{b} and a #{c.class}”
})
args(lambda{|a, b, c|
puts "Give me a #{a} and a #{b} and a #{c.class}”
})
#example2
def lambda_return
lambda { return "lambda" }.call
return "lambda_return method finished"
End
puts lambda_return
#=> lambda_return method finished
8. ‘method’ ruby method:
class Array
def iterate!(code)
self.each_with_index do |n, i|
self[i] = code.call(n)
end
end
end
def square(n)
n ** 2
end
array = [1, 2, 3, 4]
array.iterate!(method(:square))
9. Yield???
○ Placeholder for any code-block i.e. block, proc or lambda.
○ Yield lets us branch from within a method and execute some external
code, then return to the original code in the first method.
○ Blind date??
def block1
puts "Start of block1..."
yield
yield
puts "End of block1."
end
block1 {puts "yielding...”}
○ we can wrap yield with if statement as well like
yield if block_given?
○ block_given? What is this?
11. Ruby Loops/Iterators:
● Loops/Iterators in Ruby are used to execute the same block of code a
specified number of times.
● In ruby, for better understanding, we can assume to classify
looping/iterating in 2 buckets:
● Simple way to loop/iterate.
● Complex way to loop/iterate.
● Common Looping ways we use in ruby are for, while, loop, until,
while/until modifiers etc.
● Common iterating ways we use in ruby are each iterators, time iterators,
upto & step iterators, each_index iterators.
12. Ruby Looping Constructs:
○ Loop: The simplest looping constructs in ruby is ‘loop’ method.
Technically it’s an iterating block as it takes a block as input.
○ While: The while loop in Ruby is just like the standard while loop in any
other language nothing too fancy.
○ Until: The until loop is similar to the while loop but the logic is reversed.
○ While/until modifiers: Ruby also allows you to use the while and until
keywords as modifiers, which means you can put them at the end of an
expression just like you can do with the if statement.
○ For: If we discount the loop method then the for loop acts as a kind of
bridge between looping constructs and iterators in Ruby. The for loop is
still a looping construct but it acts almost like an iterator without actually
taking a block.
13. #example1-loop
loop {puts "HELLO"}
#example2-while
i=0
i=1
loop do
while i < 11
i+=1 print "#{i} "
puts i
break if i==10
i+=1
end
end
#example3-until #example4-while/until modifiers
i=1 i=0
until I > 10 puts I while i < 10
puts i
i+=1 i=0
end Puts i until I == 10
#example5-for
i=1
for i in 1..10
puts i
end
14. Ruby Iterators:
○ Iterators are methods that take blocks and execute that block as many
times as there are iterations.
○ Each iterators(something.each do ... end)
○ Iterates through each elements.
○ Times iterators(x.times do … end)
○ The times iterator is similar to you classic for loop in other languages and
will allow you to execute a loop and perform an action (according to the
block you write) x number of time
○ Upto and step iterators
○ This is also similar to for loop too, that we execute from number x up to
number y.
○ Step iterators helps to skip few steps between.
15. ‘Each’ Iterators:
array = [1,2,3,4,5,6,7,8,9,10]
array.each {|value| print "#{value} "}
(1..5).each { puts ‘We are here!’ }
(1…5).each { puts ‘we are here’}
****
Also, for does not exactly qualify as a syntax sugar for each, because they
handle the scoping of new variables differently: each makes them
disappear outside the block, whereas for makes them persist. With
experience you’re likely to find you want new variables to be confined to
the block, making each the better choice.
16. Control Flows:
○ Ruby offers conditional structures that are pretty common to modern
languages.
○ If statement.
○ If-else statement.
○ If modifier statement.
○ Unless statement.
○ Unless modifier.
○ Case statement.
case expr0
when expr1, expr2
stmt1
when expr3, expr4
stmt2
else
stmt3
end
