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Twitter: The Great Migration, the Winter of 2011

engineering.twitter.com

3 pointsby cachemoney15 anni fa0 comments

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15 anni fadiscuss

Who writes these titles?

15 anni fadiscuss

An alternative is an option type. In scala, you have the abstract type Option[T], which has implementations Some[T](value: T) and None[T].

Alternately, you have Either[A, B], with implementations Left[A](value: A), and Right[B](value: B).

So you can define a function that takes an Either[Int, ErrorMessage], rather than an Int or null. Getting a None[Int] is better than null, because it won't throw NullPointerExceptions if you access it sensibly.

Examples:

    def x2or0(i: Option[Int]): Int = i.getOrElse(0) * 2

    def x2(i: Option[Int]): Option[Int] = i.map(_ * 2)

    def x2danger(iOrPossiblyNull: Int) = i * 2
    // throws NullPointerException on null input

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> That said, how can that old game be more fun that TF2?

EMP Grenades.

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Actors had a memory leak when a lot of the formative Twitter Scala stuff happened. This lead to more usage of java concurrency primitives, which snowballed within the culture.

There's some people at Twitter who truly love and grok Scala and Scala idioms inside out, and there's some people who look at Scala as a more functional, less verbose Java.

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"It's as expressive as Ruby, but runs much faster and is easier to refactor."

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This whole thing is a bit disingenuous, because the type signature argued over is an alternate signature which no one uses, because it provides custom concatenation of Traversables. All of the provided collections have reasonable implementations of concatenation, so this implies you're inventing your own collection.

Everyone uses the alternate form: flatMap [B] (f: (A) ⇒ Traversable[B]): CC[B]. Nevertheless, I'll attempt to explain the provided signature.

If you understand Java generics, you should hopefully be able to understand this response.

A, B, and That are type parameters/generics. So they can be filled in by any type. This flatMap method exists on a trait (think Java Interface) called Traversable[A]. Traversable is similar to Iterable in java.

(f: (A) ⇒ Traversable[B]) means that this function takes one argument called f. That argument is a closure or anonymous function. The closure itself takes one argument of type A (an element in the parent Traversable[A]), and returns a Traversable[B], where B is an arbitrary type.

Skipping ahead, flatMap returns an instance of That. But what's a That? It appears to be unspecified. This is where the "(implicit bf: CanBuildFrom[List[A], B, That])" makes it's appearance.

Implicit parameters are like default arguments. "def foo(i: Int = 12)" will use the i if provided, else it will default to 12. "def foo(implicit i: Int)" will take the i given, else it will grab the first available Int in the containing scope. If you, "val c = 11; def foo(implicit i: Int) = i * 2", calling foo(1) yields 2, but calling foo() yields 22.

The object bf is an object that provides an overridable custom definition of concatenation. So when you write your custom collection, you include an instance of CanBuildFrom[List[A], B, That] in the correct scope, and it gets used for the concatenation. CanBuildFrom's type parameters say that it exists in a List[A], takes a B, and returns a That.

So yeah, in your implementation of bf, you could make it a new MyCanBuildFrom[List[A], B, FunkyCollection[B]], and do funky concatenation.

Hope that helps.

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I spent about a year as a maintainer of FlockDB, Twitter's social graph store. If you don't know, it's basically a sharded MySQL setup. One of the key pain points was optimizing the row lock over the follower count. Whenever a Charlie Sheen joins, or someone tries to follow spam us, one particular row would get blasted with concurrent updates.

Doing this in-memory in java via someAtomicLong.incrementAndGet() sounds appealing.

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Many internal tools use it.

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The economy could certainly find use for them, but perhaps not at a price above minimum wage.

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Indeed. I have over a hundred repos, and I'm useless ;)

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People are afraid of planes because if the power goes out, you die. On the ground, if the power goes out on your driverless car, you cruise to a stop.

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You can't run a Solr server because (1) present limits are 300MB RAM hard, and (2) disk is transient. There's a solr addon though.

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It drives pageviews?

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If two people independently invent something at about the same time, does that mean it's obvious to someone skilled in the art?

In those scenarios, I'd like to see both patents thrown out.

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Also, I don't know if I really want to hear about Enya from Bakersfield any more. Please do something about ad fatigue and/or inventory.

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Ironically, the guys who maintain rubygems also wrote http://rubyhitsquad.com/, in which they vocally slam another mainstream Ruby project.

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Quit trolling, that's a technicality.

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Somehow, the comment threads get flooded instead.

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This advice is potentially terrible for many/most people.

> Skip college, you can always go back.

It's much harder to get into and succeed in college later in life. You'll also be a bad fit for the college social scene, which is where many people make lifetime friends and connections.

> If you MUST go to college, DO NOT, I repeat, DO NOT get a CS degree. Go for finance, or liberal arts, even bio or chem, or some course of study where the instructors have a clue and have actually done something in that field.

I think this reveals bias from the poster.

My opinion is that you should at least start college. If you shouldn't be there, you can drop out. Find a mentor that seems to be a good fit for you. It could be a prof, a local startup founder, whatever. Make plans ahead of time (e.g. contact profs ahead of time and/or choose the university based on faculty) to secure that mentorship.

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Why be jealous? He has no traction. Copy it and do it slightly better.