Go maps in action

http://blog.golang.org/2013/02/go-maps-in-action.html

by zoowar • 13 years ago

67 19 13 years ago

blog.golang.org

gtaylor• 13 years ago

Very helpful, thanks for posting this! The parts about map declaration vs. make() vs. new() are the most valuable tidbits, I think. A lot of the rest is mostly just very handy tips and pointers.

wei2012• 13 years ago

Go everyday, but still going.

omaranto5• 13 years ago

The fact that slices cannot be used as keys in maps was, for me, a fairly big turn off.

jerf2• 13 years ago

Using a slice as a key doesn't make much sense; a slice is a fundamentally-mutable view onto an underlying array, which itself may be mutable.

Quick testing shows that you can use arrays:

    func main() {
        a := [4]int{1,2,3,4}
        m := make(map[[4]int]string)
        m[a] = "Hello"
        fmt.Println(m[[4]int{1,2,3,4}])
    }

Although that will be klunky, since the size of the array is in the type of the array. And still mutable. Mutating keys is bad.

In all my years of using maps, I can't think of when I wanted to index by something that was truly an arbitrary-length array of things. If you want to index by something like a tuple of things, declare a datatype for that purpose. What exactly are you trying to do by using a slice as a key?

omaranto5• 13 years ago

I was lazy when I complained about not be able to use slices as keys, I guess I really meant to complain that there is no arbitrary-length immutable sequence type that I can use as keys to a map (other than strings, which are sequences of characters and are allowed as keys to a map).

For an example where you might want to do this consider storing a count of the frequency with which different words follow a given n-gram (sequence of n words) in some corpus, the sort of thing you'd need to make a Markov chain nonsense text generator (like the example programs in chapter 3 of The Practice of Programming: http://cm.bell-labs.com/cm/cs/tpop/code.html).

Of course, you can always take your immutable sequences and represent them as strings, as other languages such as Perl, Awk and Lua force you to do. But I really like that I'm not forced to use such kludges in, say, Python or Haskell.

omaranto5• 13 years ago

Another application of arbitrary-length sequences is storing sparse multivariable polynomials as maps from monomials to coefficients.

shadowmint• 13 years ago

I don't really get it. It's a hash. Big deal.

I know what a hash is. Wow, Go has hashes. Yeah, I knew that too.

blinks So... yeah. I mean, it's the Go blog, so cool. Blog about things in the language, but in terms of 'interesting things about Go' or 'interesting things about tech I expect to see on hacker news frontpage' this is pretty much a 0 for me...

enneff• 13 years ago

So an article titled "Go maps in action" is about Go maps and... you're underwhelmed? Dissatisfied? This is an article for people who want to learn about Go maps. I'm not sure what you expected.

You would be surprised how valuable these kinds of "entry level" articles are. I get more grateful mail about the basic articles than I do the advanced ones, because the audience is so much wider.

So, not for you I guess.

est• 13 years ago

reminds me of people defending reposts on reddit.

Yeah I've never seen it three minutes ago on frontpage, so the repost is OK for me and people like me.

Maps in Go is definitely a good lesson for hackers who doesn't know about maps...

Go maps in action

Related Stories