Ruby objects with a telephone
What is a callable object?
What is an anonymous function?
Anonymous function is the one that is not bound to an identifier.
Object is callable if it responds to the #call method.
block
proc
Proc
lambda
->
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{ }
do/end
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BLOCKS (1/3)
BLOCKS (2/3)
Wikipedia describes blocks as anonymous functions.
Block is not a function, it is a complementary method syntax.
BLOCKs (3/3)
To execute a block from within a method, you use yield keyword. It is not possible to #call a block!
Syntax:
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{} - one-liners -
do/end - multi-liners
PROCs (1/3)
Proc class
procs (2/3)
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language construct for using closures
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constructors:
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Proc.new {} -
proc {} - preferred by Ruby style guide
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procs (3/3)
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pass arguments through 'pipes'
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proc { |arg1, arg2| p arg1, arg2 }
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will "answer" when called with:
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#call() - OK
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#[] - NOT OK
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#.() - HORRIBLE
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lambdas
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special, much stricter, instance of a Proc class
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constructors and parameters:
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lambda { |arg1, arg2| } -
->(arg1, arg2) {}
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#call() it
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Proc#lambda?
#funfact -'proc' and 'lambda' are not keywords but Kernel methods.
The difference(s)
| Handles | arguments | return keyword |
|---|---|---|
| proc | loosely | passes control to the outer scope |
| lambda | strictly | passes control to a current scope |
Lambdas behave like methods.
usage of '&' (1/2)
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inside a method definition:
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denotes that identifier it binds is not an argument, but a proc object
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def foo(a, b, &block)
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on a callers side:
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array.map(&:map)
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invokes #to_proc on a object passed
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Still confused?! It's OK..
usage of '&' (2/2)
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STEP foo { puts "Within a block!" } -
STEP proc { puts "Within a block!" } -
STEP def foo(&block) block.call end
rails usage examples (1/3)
In the wild, Ruby can even become "JQuerish".
RAILS usage examples (2/3)
Doing some caching.
RAILS usage examples (3/3)
You are probably using it already.
methods as objects
Methods can become object as well: m = bar.method(:foo) # m is a method #foo m.call # callable object
resources
Ruby objects with a telephone
By Dario Daic
Ruby objects with a telephone
In this presentation we will take a look at how Ruby implements closures using a Proc class. We are also going to make distinctions between blocks and procs, and procs and lambdas as well.
