Add Data.Aeson.Key.length

[sjshuck]

The JSON spec requires UTF-8 encoding (source). So the notion of the length of a key, defined as number of code points, seems well-defined.

The best way I've found is Data.Text.length . Data.Aeson.Key.toText which requires keeping up with current (unspecified) implementation to avoid extra work, plus adding text to explicit dependencies if not already there.

Happy to toss in a PR if deemed reasonable.

[phadej]

Why you need to know the key length.

If you do something text-y with keys, then IMO conversion to Text is a way to go. Generally keys are "opaque" values...

EDIT: also length is O(n) operation, and I feel uncomfortable adding "slow" functions. I bet someone will then ask whether it can be made O(1) etc, a development I don't want to engage with.

[sjshuck]

Why you need to know the key length.

For example, I want to validate labels to add to a resource, and label keys are capped at 63 characters, but I don't want to do any more analysis than that, and I'm only passing ByteStrings around and don't want to mess with Text.

Generally keys are "opaque" values

which are specified as UTF-8, that is a ceiling to our opacity

I feel uncomfortable adding "slow" functions

Aeson is already generating intermediate data Value = ... | String !Text | .... And length of UTF-8 is inherently O(n).

I dont want to engage with

You are already engaging with this small PR, I imagine you will have no problem saying "no" to that person.

[phadej]

String !Text 

that is textual value. Those are not keys.

SOrry. I think the way to do it is to explicitly convert to Text.