Stockholm Ruby 2013-10-30

# Kim Persson

![Kim](https://raw.github.com/Lavinia/iYield/master/noting.png "Noting")

.center[Github: [Lavinia](https://github.com/Lavinia/)

Twitter: [@Lavinia666](https://twitter.com/Lavinia666)

Ruby developer at Barsoom: [http://barsoom.se](http://barsoom.se)]

---

# Nemah
## A real princess with a
###gigantic
## apetite

![Nemah](https://raw.github.com/Lavinia/iYield/master/Nemah.jpg "Om nom nom")

---

# Rails
## layouts/application.html.erb

```ruby
<!DOCTYPE html>
<html>
<head>
  <title>Rubytalk</title>
  <%= stylesheet_link_tag    "application", media: "all" %>
  <%= javascript_include_tag "application" %>
  <%= csrf_meta_tags %>
</head>
<body>

<%= yield %>

</body>
</html>
```
---

# WAT !??
![Nemah](https://raw.github.com/Lavinia/iYield/master/NemahNom.jpg "Om nom nom")
---

# Blocks

```ruby
hungry_horse { puts 'Omnomnom...' }

hungry_horse do
  puts 'Omnomnom...'
end

def hungry_horse
  yield
end

```
```ruby
# 'Omnomnom...'

```
---

# Blocks
## (cont.)

```ruby
def doubler(number)
  yield number * 2
  puts "doubled!"
end

doubler(5) do |result|
  puts result
end

```

```ruby
# 10
# doubled!
```
---

# Blocks
## precedence

```ruby
doubler 5 do |result|
  puts result
end
```

```ruby
# 10
```
---
# Blocks
## precedence

```ruby
doubler 5 do |result|
  puts result
end
```

```ruby
# 10
```

```ruby
doubler 5 { |result| puts result }
```

```ruby
# SyntaxError: (irb):5: syntax error, unexpected '{',
# expecting end-of-input
```

---

# Blocks
## (cont.)

```ruby
def method_that_can_go_horribly_wrong
  #...
  raise StandardError, "OUCH!"
rescue => error
  yield error
end

method_that_can_go_horribly_wrong do |error|
  #some error handling code
end
```

---

# Blocks
## (cont.)

```ruby
def method_that_can_go_horribly_wrong
  #...
  raise StandardError, "OUCH!"
rescue => error
  yield error
end

method_that_can_go_horribly_wrong
```

```ruby
# LocalJumpError: no block given (yield)
```
---

# Blocks
## (cont.)

```ruby
def method_that_can_go_horribly_wrong
  #...
  raise StandardError, "OUCH!"
rescue => error
  yield error if block_given?
end

method_that_can_go_horribly_wrong do |error|
  #some error handling code
end
```
---

# Blocks
## (cont.)

```ruby
def method_that_can_go_horribly_wrong
  #...
  raise StandardError, "OUCH!"
rescue => error
  if block_given?
    yield error
  else
    raise #reraise last error
  end
end

method_that_can_go_horribly_wrong do |error|
  #some error handling code
end
```
---

# Proc

```ruby
error_handler = Proc.new { |error| # error handling code... }

error_handler = proc do |error|
  # error handling code...
end
```
---
# Proc
```ruby
error_handler = proc do |error|
  # error handling code...
end

def method_that_can_go_horribly_wrong(error_handler)
  #...
  raise StandardError, "OUCH!"
rescue => error
  error_handler.call(error)
end

method_that_can_go_horribly_wrong(error_handler)
```

---

# Proc

```ruby
error_handler = proc do |error|
  # error handling code...
end

def method_that_can_go_horribly_wrong(error_handler)
  #...
  raise StandardError, "OUCH!"
rescue => error
  error_handler.call(error)
end

method_that_can_go_horribly_wrong(error_handler)
```
```ruby
error_handler.call(error)
error_handler.yield(error)
error_handler.(error)
error_handler[error]
```

---

# Proc
## proc to block

```ruby
error_handler = Proc.new { |error| # error handling code... }

def method_that_can_go_horribly_wrong
  #...
  raise StandardError, "OUCH!"
rescue => error
  if block_given?
    yield error
  else
    raise
  end
end

method_that_can_go_horribly_wrong(&error_handler)
```

---

# Proc
## #to_proc

```ruby
[1,2,3].inject(&:+)
```
```ruby
# 6
```
---

# Proc
## #to_proc

```ruby
[1,2,3].inject(&:+)
```

```ruby
# 6
```

```ruby
[1,2,3].inject do |sum, number|
  sum + number
end

```

---

# Proc
## block to proc

```ruby
def method_that_can_go_horribly_wrong(&error_handler)
  #...
  raise StandardError, "OUCH!"
rescue => error
  error_handler.call(error)
end

method_that_can_go_horribly_wrong do |error|
  #some error handling code
end
```
---
# Proc

```ruby
null_value? = proc { |value| value.nil? }

null_value?.call()
```
```ruby
# true
```

---
# Lambda

```ruby
proc {}
# #<Proc:0x007fc079b0d948@(irb):27>

lambda {}
# #<Proc:0x007fc079b06d00@(irb):28 (lambda)>
```

---
# Lambda

```ruby
proc {}
# #<Proc:0x007fc079b0d948@(irb):27>

lambda {}
# #<Proc:0x007fc079b06d00@(irb):28 (lambda)>
```

```ruby
feed = ->(horse, fodder) do
  puts "Feeding #{horse} with #{fodder}"
end

feed.call('Nemah')
```

```ruby
# ArgumentError: wrong number of arguments (1 for 2)
```
---

# Proc and Lambda
## utility methods

```ruby
feed.arity
```
```ruby
# 2
```
---

# Proc and Lambda
## utility methods

```ruby
feed.arity
```
```ruby
# 2
```
```ruby
feed.lambda?
```
```ruby
# true
```
---

# Proc and Lambda
## utility methods

```ruby
lambda { |mandatory, optional = 1, *other| code }.parameters
```
```ruby
# [[:req, :mandatory], [:opt, :optional], [:rest, :other]]
```

---
# Proc and Lambda
## utility methods

```ruby
lambda { |mandatory, optional = 1, *other| code }.parameters
```
```ruby
# [[:req, :mandatory], [:opt, :optional], [:rest, :other]]
```

```ruby
proc { |mandatory, optional = 1, *other| code }.parameters
```
```ruby
# [[:opt, :mandatory], [:opt, :optional], [:rest, :other]]
```

---
# Proc and Lambda
## break

```ruby
printer = lambda do |x|
  puts x
  break
end

printer.call('Hi')
```
```ruby
# Hi
```

---
# Proc and Lambda
## break

```ruby
printer = lambda do |x|
  puts x
  break
end

printer.call('Hi')
```
```ruby
# Hi
```

```ruby
printer = proc do |x|
  puts x
  break
end

printer.call('Hi')
```
```ruby
# Hi
# LocalJumpError: break from proc-closure
```

---

# Proc and Lambda
## break and iterators

```ruby
printer = proc do |x|
  puts x
  break
end

(1..3).each { |i| printer.call(i) }
```
```ruby
# 1
```

---

# Proc and Lambda
## break and iterators

```ruby
printer = proc do |x|
  puts x
  break
end

(1..3).each { |i| printer.call(i) }
```
```ruby
# 1
```
```ruby
printer = lambda do |x|
  puts x
  break
end
(1..3).each { |i| printer.call(i) }
```
```ruby
# 1
# 2
# 3
```
---
# Proc and Lambda
## return

```ruby
def greeting_commander_riker
  name = proc { return 1 }.call
  puts "Hi there number #{name}!"
end
```
```ruby
# 1
```
---
# Proc and Lambda
## return

```ruby
def greeting_commander_riker
  name = proc { return 1 }.call
  puts "Hi there number #{name}!"
end
```
```ruby
# 1
```

```ruby
def greeting_commander_riker
  name = lambda { return 1 }.call
  puts "Hi there number #{name}!"
end
```
```ruby
# 'Hi there number 1!'
```

---
# Closures

```ruby
def method_that_can_go_horribly_wrong(error_handler)
  # ...
  raise StandardError, "OUCH!"
rescue => error
  error_handler.call(error)
end
```
---

# Closures

```ruby
def method_that_can_go_horribly_wrong(error_handler)
  # ...
  raise StandardError, "OUCH!"
rescue => error
  error_handler.call(error)
end

class MagicLogger
  def self.logger(header_message)
    magic_logger = new
    lambda { |error| magic_logger.log(header_message, error) }
  end

def log(header_message, error)
    puts header_message
    puts error.message
  end
end

error_handler = MagicLogger.logger('Something went wrong!')
method_that_can_go_horribly_wrong(error_handler)
```
---
# We started with this...

<%= yield %>

</body>
</html>
```
---
# WAT!??
![Nemah](https://raw.github.com/Lavinia/iYield/master/NemahNom.jpg "Om nom nom")
---
# ...and we still might feel a bit like WAT!??
![Nemah](https://raw.github.com/Lavinia/iYield/master/NemahNom.jpg "Om nom nom")

---
class: center, middle, white

![Barsoom](http://barsoom.se/barsoom.png)

We are hiring! => [http://barsoom.se/job](http://barsoom.se/job)

---