3.4. SHOULD be mindful of the garbage collector — Incorrect example

[Aivean]

https://github.com/alexandru/scala-best-practices/blob/master/sections/3-architecture.md#34-should-be-mindful-of-the-garbage-collector

someCollection
 .filter(Set(a,b,c).contains)
 .map(_.name)

First of all, this creates a Set every single time, on each element of our collection.

This is not true. Set is created only once and then its contains function is passes as an argument to filter method. This function is then invoked per each element of someCollection.

Compare to similar code snippet:

someCollection
 .filter(Set(a,b,c).contains(_))
 .map(_.name)

In this case a wrapping function is be created around Set(a,b,c).contains, something like x:Int => Set(a,b,c).contains(x) and this function is then passed as an argument for filter. Set is created inside wrapping function, so it's creation is performed once per element of someCollection.

---

Also, in this item it is worth to mention eagerness of monadic operations on scala collections.
In provided example:

  .filter(bySomething)
  .map(toSomethingElse)
  .filter(again)
  .headOption

by default each step produces new collection (opposite to laziness of C#'s linq), which produces lots of garbage when chain is long.

Easy way (though no obvious) is to add .view at the beginning of the chain. This makes whole chain lazy.

[alexandru]

This is not true. Set is created only once and then its contains function is passes as an argument to filter method. This function is then invoked per each element of someCollection.

You're right. Will fix.

Easy way (though no obvious) is to add .view at the beginning of the chain. This makes whole chain lazy.

Views are considered deprecated. Iterable is better.

[Aivean]

Views are considered deprecated. Iterable is better.

Sorry, can you provide a source for that statement? Quick search over internet gave nothing, as well as scaladocs for scala 2.11.6.