New filter for hashes where the key is an ID of some kind with an attached value

[AaronLasseigne]

In #459 and #531 we see a case that isn't easily handled within ActiveInteraction. It's the situation where a has is used not as a group of information but as a lookup where the key is some unique ID and the values are... whatever.

I think I'm going to add a new filter called lookup to handle this. It would work by accepting any key and then validating the value if a block is given. It would be the same way the array filter works.

lookup :cities do
  integer
end

Then you could pass a hash with a matching format:

cites: { Tokyo: 37_468_000, Delhi: 28_514_000, ... } 

Questions:

1. Should there be a way to validate keys?

[AaronLasseigne]

Maybe hashmap instead of lookup?

[shettytejas]

@AaronLasseigne I do like the name lookup more instead of hashmap. As of key validation, I do think that could be helpful.

How about a syntax something like this?

lookup[string] :cities do
  integer
end

So if anyone wants to use the key validation, they can by passing the data type of the key, else they can ignore.

P.S: Thinking a bit more after a while, how about something like this? The name hashmap would also make sense here:

hashmap[string, integer] :cities