Keys

Create a type that will be used to query the counter state.
Also create a function to construct this type from the ABI.
Keys are vectors of words so here we create a vector with a single word.

#![allow(unused)]
fn main() {
#[derive(Clone)]
pub struct CounterKey(pub Vec<Word>);

pub fn counter_key() -> CounterKey {
    let keys: Vec<_> = storage::keys().counter().into();
    CounterKey(keys.first().unwrap().clone())
}
}

Here, we're extract the storage key for the storage variable counter by using the method counter().