Constraints and pre-post cast

[pwalsh]

From @roll

It’s really critical for simplicity of implementations and we had an extensive discussion on it with @pwalsh and @akariv

Having pre-cast constraint really complicates simple data flow for implementations - null value, cast value, check constraints. With pre-cast pattern now we have a special case.

It also creates at lot of friction on conceptual level. Consider JSON data - it’s already typed and has never been a string so how to apply the pattern constraint on it?

So my main suggestion to Table Schema spec:

Please write that pattern constraint applied only to string type

It’s already implemented in Python/JavaScript and I’m not sure there is any user interest in having pattern for other types. So no reason to complicate our life)