fix KVOp types

[alicebob]

It was not possible to use KVSet as a transaction type:

./main.go:94: cannot use api.KVSet (type api.KVOp) as type string in field value

[slackpad]

Thanks for the PR! Noted one small thing.

[slackpad]

You shouldn't need to repeat the KVOp here, the first one will set them all. It was the change to the struct below that fixed this.

[alicebob]

afaik that only works for iota assignments. This is the output of gist https://gist.github.com/alicebob/aa17022b6f1d6f8fbf3337e2c178c858

KVSet: main.KVOp
KVDelete: main.KVOp
KVDeleteCAS: string
KVDeleteTree: string

[alicebob]

The relevant piece from the Go language specs:

Within a parenthesized const declaration list the expression list may be omitted from any but the first declaration. Such an empty list is equivalent to the textual substitution of the first preceding non-empty expression list and its type if any. Omitting the list of expressions is therefore equivalent to repeating the previous list.

https://golang.org/ref/spec#Constant_declarations

Since the expression isn't empty (it's a string) you need to repeat the type.

[slackpad]

Hi @alicebob that clause in the spec is to allow for iota, basically. The section before that talks about the type being optional, not the expression part. I tried it in the Go playground and it worked fine with just the one type, and we do that in lots of other places in Consul :-)

[alicebob]

Morning @slackpad. Sorry to make such a fuzz about a few lines, but it's not the same thing. The types don't get copied over; it happens to work because the definitions without a type are untyped string constants. Not specifying a type at all also works fine:

type KVOp string

const (
    KVSet          = "set"
    KVDelete       = "delete"
...

If you only add a KVOp type for KVSet then KVSet will be a typed string, but KVDelete will still be untyped. So I would either add the type on every line, or not at all.

Have a look at my Gist posted above, and reread the 'String constants' part from https://blog.golang.org/constants .

[slackpad]

Doh thanks for the correction and sorry I missed the gist output above - my understanding was definitely incorrect!