Getting Closure: Ruby's Blocks, Procs and Lambdas

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Getting Closure Ruby Blocks, Procs and Lambdas Tuesday, May 28, 13

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Johnny Boursiquot (boar-cee-co) Technologist Tech Director/Software Architect at a local interactive agency (MAARK) @jboursiquot / jboursiquot.com Tuesday, May 28, 13

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What we’ll talk about Closures - What they are, their value Blocks Procs Lambdas Where to go (literally) from here Tuesday, May 28, 13

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So, what’s a “closure” anyway? Tuesday, May 28, 13

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A closure is... A function or method that can be passed around like an object It remembers variables that were in scope when it was created Tuesday, May 28, 13

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Let’s take a step back... Tuesday, May 28, 13

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December 2003 Tuesday, May 28, 13

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Notable Events Tuesday, May 28, 13

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Barry White dies Tuesday, May 28, 13

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“Matz” has an interview... Tuesday, May 28, 13

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December 22, 2003 A Conversation with Yukihiro Matsumoto, Part III http://www.artima.com/intv/closures.html Tuesday, May 28, 13

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“Blocks are basically nameless functions...Basically, you can pass a nameless function to another function, and then that function can invoke the passed-in nameless function.” Tuesday, May 28, 13

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“Many other languages do this style of programming. In Ruby, the difference is mainly a different kind of syntax...” Tuesday, May 28, 13

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Blocks Tuesday, May 28, 13

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Block Syntax Tuesday, May 28, 13

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Well, why is this important? Tuesday, May 28, 13

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Block Syntax Sure, it works. Looks familiar. But, it’s full of coupling. Tuesday, May 28, 13

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Block Syntax Block helps you decouple logic from iteration They take parameters -- like methods They appear after method invocation -- as if an additional parameter to your method call Tuesday, May 28, 13

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Block Syntax Block called once for each iteration of array Each element passed into block as a variable Variables deﬁned inside block are local to that block Tuesday, May 28, 13

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Block Syntax “yield” is used in methods that accept blocks as parameters to transfer control to the block and back Tuesday, May 28, 13

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Block Rules Parameters to a block are always local to that block, even if variable names are shared with the outside. Tuesday, May 28, 13

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Block Rules You can deﬁne block-local variables by putting them after a semicolon in the block's parameter list. Tuesday, May 28, 13

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Hmmm.... How can we not repeat ourselves whenever we need to double a number? Tuesday, May 28, 13

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Back to Closures Tuesday, May 28, 13

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A closure is... A function or method that can be passed around like an object It remembers variables that were in scope when it was created Tuesday, May 28, 13

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Procs Tuesday, May 28, 13

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Proc Syntax We turn the logic we need into a Proc so we can pass it around We use “&” when calling our collect method to convert the Proc back into a block because it expects one Tuesday, May 28, 13

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Proc’s Beneﬁts Unlike blocks, they are objects that can be passed around Unlike blocks, they can be called upon multiple times, making our code DRYer Tuesday, May 28, 13

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Lambdas Tuesday, May 28, 13

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Lambda Syntax Tuesday, May 28, 13

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So...what’s the difference? Tuesday, May 28, 13

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Procs vs Lambdas Lambdas check the number of arguments passed in. Procs do not. Procs ignore any missing arguments, assigning nil to them. Lamdas return to the calling method, Procs return immediately without going back to the caller. Tuesday, May 28, 13

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Behavior of Missing Arguments Tuesday, May 28, 13

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Behavior of Return Statements Calling return from inside a proc will return from calling method Calling return from lambda will return only from the lambda Tuesday, May 28, 13

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Not Covered in Depth Tuesday, May 28, 13

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Closure Scope Retention Create a copy of all variables at time of deﬁnition Retain reference to variables (Ruby’s uses this method) Tuesday, May 28, 13

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We’ll save that for a Project Night 1st Tuesdays of the Month Tuesday, May 28, 13