AWS cloudwatch dynamically list metrics and there infomation

Right, so I am trying to get a list of metric_names for a particular namespace (I'd rather it be for an object, but I'm working with what I've got) using AWS Ruby sdk, and cloudwatch has the list_metrics function, awesome!..

Except that list_metrics doesn't return what unit's and statistics a metric supports which is a bit stupid as you need both to request data from a metric.

If you're trying to dynamically build a list of metrics per namespace (which I am) you won't know what unit's or statistics a particular metric might support without knowing about the metrics before hand which makes using list_metrics to dynamically get a list of metrics pointless.

How do I get around this so I can build a hash in the correct format containing the metrics for any namespace without knowing anything about a metric before hand except for the hash structure.

Also why is there not a query for what metrics an object (dynamo,elb,etc) has?

It seems a logical thing to have because a metric does not exist for an object unless it's actually spat out data for that metric at least once (so I've been told); which means even if you have a list of all the metrics a namespace supports, it doesn't mean that an object within the namespace will have those metrics.