The document discusses Ruby's === operator and how it can be used to emulate pattern matching. It explains how === is used internally by classes like Integer, Regexp, and Range to check object equality. It then shows how to write custom matcher classes and procedures to select objects based on multiple criteria, like selecting people objects that match a name regex and fall within an age range. Finally, it provides examples of pattern matching libraries like Qo that build on these concepts.

1. === BLACK MAGIC
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2. WHO AM I?
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3. WHO AM I?
My name is Brandon Weaver
I work at Square
I love Ruby, Javascript, and Lemurs
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4. HOW ===
WORKS
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5. HOW === WORKS
===
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6. HOW === WORKS
/^f/ === 'foo'
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7. HOW === WORKS
def ===(v)
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8. HOW === WORKS
/^f/.===('foo')
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9. HOW === WORKS
class Integer
def ===(v)
self == v
end
end
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10. HOW === WORKS
class Regexp
def ===(v)
match? v
end
end
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11. HOW === WORKS
Regexp = match?
Range = include?
Class = is_a?
Proc = call
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12. HOW === WORKS
/^f/ === 'foo'
(1..10) === 1
String === 's'
-> a {a+1} === 2
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13. WHERE’S ===
HIDING?
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14. WHERE’S === HIDING?
case value
when String
'string'
when Integer
0
end
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15. WHERE’S === HIDING?
[1, 2, 3.0].grep(Integer)
# => [1, 2]
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16. WHERE’S === HIDING?
[1, 2, 3.0].all?(Integer)
# => false
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17. WHAT’S A
CLOSURE?
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18. WHAT’S A CLOSURE?
adder = proc { |a|
proc { |b| a + b }
}
add3 = adder.call(3)
[1,2,3].map(&add3)
# => [4,5,6]
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19. WHAT’S A CLOSURE?
adder = proc { |a|
proc { |b| a + b }
}
add3 = adder.call(3)
[1,2,3].map(&add3)
# => [4,5,6]
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20. WHAT’S A CLOSURE?
adder = proc { |a|
proc { |b| a + b }
}
add3 = adder.call(3)
[1,2,3].map(&add3)
# => [4,5,6]
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21. WHAT’S A CLOSURE?
adder = proc { |a|
proc { |b| a + b }
}
add3 = adder.call(3)
[1,2,3].map(&add3)
# => [4,5,6]
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22. WHAT’S A CLOSURE?
adder = proc { |a|
proc { |b| a + b }
}
[1,2,3].map(&adder.call(3))
# => [4,5,6]
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23. EMULATING
PATTERN MATCHING
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24. EMULATING PATTERN MATCHING
query = proc { |*matchers|
proc { |target|
matchers.all? { |m| m === target }
}
}
[1,1.0,'s'].select(&query.call(
Integer, 1..10, :odd?.to_proc
))
# => [1]
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25. EMULATING PATTERN MATCHING
query = proc { |*matchers|
proc { |target|
matchers.all? { |m| m === target }
}
}
[1,1.0,'s'].select(&query.call(
Integer, 1..10, :odd?.to_proc
))
# => [1]
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26. EMULATING PATTERN MATCHING
query = proc { |*matchers|
proc { |target|
matchers.all? { |m| m === target }
}
}
[1,1.0,'s'].select(&query.call(
Integer, 1..10, :odd?.to_proc
))
# => [1]
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27. EMULATING PATTERN MATCHING
query = proc { |*matchers|
proc { |target|
matchers.all? { |m| m === target }
}
}
[1,1.0,'s'].select(&query.call(
Integer, 1..10, :odd?.to_proc
))
# => [1]
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28. EMULATING PATTERN MATCHING
query = proc { |*matchers|
proc { |target|
matchers.all? { |m| m === target }
}
}
[1,1.0,'s'].select(&query.call(
Integer, 1..10, :odd?.to_proc
))
# => [1]
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29. EMULATING PATTERN MATCHING
people = [
{name: 'Foo', age: 42},
{name: 'Bar', age: 20},
{name: 'Baz', age: 30},
{name: 'Boo', age: 10},
]
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30. EMULATING PATTERN MATCHING
query = proc { |**matchers|
proc { |target|
matchers.all? { |k,m|
m === target[k]
}
}
}
people.select(&query.call(
name: /^Foo/, age: 40..50
))
# => [{name: 'Foo', age: 42}]
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31. EMULATING PATTERN MATCHING
query = proc { |**matchers|
proc { |target|
matchers.all? { |k,m|
m === target[k]
}
}
}
people.select(&query.call(
name: /^Foo/, age: 40..50
))
# => [{name: 'Foo', age: 42}]
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32. EMULATING PATTERN MATCHING
query = proc { |**matchers|
proc { |target|
matchers.all? { |k,m|
m === target[k]
}
}
}
people.select(&query.call(
name: /^Foo/, age: 40..50
))
# => [{name: 'Foo', age: 42}]
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33. EMULATING PATTERN MATCHING
query = proc { |**matchers|
proc { |target|
matchers.all? { |k,m|
m === target[k]
}
}
}
people.select(&query.call(
name: /^Foo/, age: 40..50
))
# => [{name: 'Foo', age: 42}]
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34. EMULATING PATTERN MATCHING
query = proc { |**matchers|
proc { |target|
matchers.all? { |k,m|
m === target[k]
}
}
}
people.select(&query.call(
name: /^Foo/, age: 40..50
))
# => [{name: 'Foo', age: 42}]
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35. EMULATING PATTERN MATCHING
people_objects = people.map { |v|
OpenStruct.new(v)
}
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36. EMULATING PATTERN MATCHING
query = proc { |**matchers|
proc { |target|
matchers.all? { |k,m|
m === target.public_send(k)
}
}
}
people_objects.select(&query.call(
name: /^Foo/, age: 40..50
))
# => [OS(name: 'Foo', age: 42)]
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37. EMULATING PATTERN MATCHING
query = proc { |**matchers|
proc { |target|
matchers.all? { |k,m|
m === target.public_send(k)
}
}
}
people_objects.select(&query.call(
name: /^Foo/, age: 40..50
))
# => [OS(name: 'Foo', age: 42)]
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38. CLASS
WRAPPERS
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39. CLASS WRAPPERS
class Query
def initialize(*ms) @ms = ms end
def to_proc
proc { |v| self.call(v) }
end
def call(v)
@ms.all? { |m| m === v }
end
alias_method :===, :call
end
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40. CLASS WRAPPERS
class Query
def initialize(*ms) @ms = ms end
def to_proc
proc { |v| self.call(v) }
end
def call(v)
@ms.all? { |m| m === v }
end
alias_method :===, :call
end
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41. CLASS WRAPPERS
class Query
def initialize(*ms) @ms = ms end
def to_proc
proc { |v| self.call(v) }
end
def call(v)
@ms.all? { |m| m === v }
end
alias_method :===, :call
end
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42. CLASS WRAPPERS
class Query
def initialize(*ms) @ms = ms end
def to_proc
proc { |v| self.call(v) }
end
def call(v)
@ms.all? { |m| m === v }
end
alias_method :===, :call
end
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43. CLASS WRAPPERS
[1,1.0,’s’].select(&Query.new(
Integer, 1..10, :odd.to_proc
))
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44. CLASS WRAPPERS
case 1
when Query.new(Integer, 1..10)
# …
else
end
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45. IN THE WILD
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46. IN THE WILD - QO (PATTERN MATCHING)
people.map(&Qo.match { |m|
m.when(age: 13..19) { |person|
"#{person.name} is a teen"
}
m.else { |person|
"#{person.name} is #{person.age} years old"
}
})
people.select(&Qo.and(age: 10..19, name: /^F/))
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47. IN THE WILD - QO (PATTERN MATCHING)
people.map(&Qo.match { |m|
m.when(age: 13..19) { |person|
"#{person.name} is a teen"
}
m.else { |person|
"#{person.name} is #{person.age} years old”
}
})
people.select(&Qo.and(age: 10..19, name: /^F/))
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48. IN THE WILD - SF (BLACK MAGIC)
(1..100).map(&Qo.match { |m|
m.when(Sf % 15 == 0) { 'FizzBuzz' }
m.when(Sf % 5 == 0) { 'Fizz' }
m.when(Sf % 3 == 0) { 'Buzz' }
m.else { |n| n }
})
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49. WRAPPING UP
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50. @keystonelemur