3 ms·

Going from java to ruby these functions were the most obvious improvement for my day to day coding.

• mrgriscom 14y ago
  I agree. These functions have completely changed how I approach algorithms and data manipulation. I was super-excited to learn Go, but it was a showstopper to discover that Go's lack of support for generics effectively made this pattern of programming impossible. Major disappointment.
  • 0x0 14y ago
    Genuinely curious, what do generics have to do with this?
    • gridaphobe 14y ago
      The type of map is `(a -> b) -> [a] -> [b]`, which means that map takes a function from any type `a` to any type `b` and a list of `a`s, and returns a list of `b`s. Generics, aka parametric polymorphism, are required for this because the definition of map makes no assumptions on what types `a` and `b` will be instantiated to.
      • DougWebb 14y ago
        What does "from any type 'a' to any type 'b'" mean? That sounds like a range of types, but I don't see how that makes sense. Did you just mean that the map converts from 'a' to 'b'?
        • FreeFull 14y ago
          a and b are placeholders (type variables). They can be any type, for example Integer, or a Float. It doesn't matter. [a] is a list of a, [b] is a list of b. Map takes a function that takes an a and returns a b, and applies it to every element of [a] in order to produce the [b]. An example usage is map lessThanThree [1,2,3,4] In this case, map takes a function where a is an integer, and b is a boolean, then takes a list of integers and produces a list of booleans. The result is [True,True,False,False]
          • jjaredsimpson 14y ago
            It's also illuminating to note that haskell curries function application. This allows us to think of map as a function of one argument. map :: (a -> b) -> ([a] -> [b]) so instead of thinking that map takes a function and a list and applies that function to the list, we can think that map takes a function and "lifts" that functions argument and result types to the list type. This thinking leads us directly to Functors and fmap
• GlennS 14y ago
  I recently started a Java job after having avoided it in favour of better languages for some time. I've found the Google Guava library makes Java programming a lot more bearable: https://code.google.com/p/guava-libraries/ https://code.google.com/p/guava-libraries/ Thinks that will make your life easier * Collections2.filter() -> this is just filter() * Collections2.transform() -> this is map() * ImmutableMap.of() -> for when you need to create a quick lookup You still have to make an anonymous inner class every time you want to pass a function as an argument though.
  • ollysb 14y ago
    Yeah, I actually wrote some similar functions for java when I first started experimenting with ruby on the side. I agree it's a big improvement on for loops but there's still a lot of line noise; the anonymous class(as you mention) and having to passing the collection into a static method which is never great. Importing Collections2 statically does make it a bit more pleasant though.