Cast to "type" type

[philrz]

Repro is with Zed commit e6be73e.

tl;dr

I found myself wanting to perform this cast, but it's not implemented yet.

$ zq -version
Version: v1.8.1-64-ge6be73ee

$ echo '"<int64>"' | zq -z 'yield type(this)' -
error("cast to type not implemented")

Details

The high level use case is that I want to cast values to richer Zed types so I can use them in certain functions. I'll explain by first using a non-type example.

$ echo '{addr:"1.2.3.4", net:1.0.0.0/8}' | zq -z 'yield cidr_match(net, ip(addr))' -
true

i..e, addr started as a string, so I turned it into an ip so I could use it as an arg to cidr_match().

That worked, so let's start from this:

$ echo '{value:1, dest_type:<int8>}' | zq -z 'yield cast(value, dest_type)' -
1(int8)

That works since dest_type was a type type out of the gate. But what if I do this?

$ echo '{value:1, dest_type:"<int8>"}' | zq -z 'yield cast(value, type(dest_type))' -
error({message:"shaper type argument is not a type",on:error("cast to type not implemented")})

@mattnibs did point out this works, though.

$ echo '{value:1, dest_type:"<int8>"}' | zq -z 'yield cast(value, parse_zson(dest_type))' -
1(int8)

As a user, I'd not thought to try that since the other casting functions work the way they do.

[philrz]

Verified in Zed commit 8a48163.

The cast attempted in the repro steps now succeeds.

$ zq -version
Version: v1.12.0-28-g8a48163f

$ echo '"<int64>"' | zq -z 'yield type(this)' -
<int64>

Thanks @mattnibs!