A two-line tree in Groovy

tree.md

Two line Tree in Groovy

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Update!

Wow... Kiyotaka Oku's fork of this shows how to do it in one line :-)

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The other day, I saw Harold Cooper's One-line tree in Python via autovivication, and wondered if the same thing was possible in Groovy.

The answer is yes! But you need to define the variable tree before you can assign it to the self-referential withDefault closure, hence with Groovy, it's a two-line solution ;-)

Anyway, given:

def tree
tree = { -> return [:].withDefault{ tree() } }

We can then do:

users = tree()
users.harold.username = 'hrldcpr'
users.yates.username = 'tim'

And printing this out

println new groovy.json.JsonBuilder( users ).toPrettyString()

gives:

{
    "harold": {
        "username": "hrldcpr"
    },
    "yates": {
        "username": "tim"
    }
}

@hrhristov Yeah, given:

def tree = { [:].withDefault{ owner.call() } }

And some JSON representing Users:

def json = '''{
             |   "harold": {
             |        "username": "hrldcpr"
             |    },
             |    "yates": {
             |        "username": "tim"
             |    }
             |}'''.stripMargin()

Then we can read it into a Map using:

def users = new groovy.json.JsonSlurper().parseText( json )

However, if we want to add new branches automatically to this as if it were a tree (as above), then we need something to take a map and decorate all the "branches" as trees

def mapToTree = { map -> map.inject( tree() ) { m, n ->
    m << [ (n.key):n.value instanceof Map ? owner.call( n.value ) : n.value ]
  }
}

Then, we can get the users like so:

def users = mapToTree( new groovy.json.JsonSlurper().parseText( json ) )

And add to it as before:

users.bert.username = 'woo'
println new groovy.json.JsonBuilder( users ).toPrettyString()

which now prints:

{
    "harold": {
        "username": "hrldcpr"
    },
    "yates": {
        "username": "tim"
    },
    "bert": {
        "username": "woo"
    }
}

Hope this helps :-)

Awesome! Thanks! :)

@timyates The above solution is also Groovi-er ;)