Golang quick initialize sql.Null*

Question

Here is small code snippet that workds well:

package main

import "fmt"
import "database/sql"


type Something struct {
    Int64 int64
    Valid bool
}

func main() {
    var s = sql.NullInt64{1, true}  // <- unkeyed fields warning
    var s1 = Something{1, true}
    fmt.Printf("Hello, %#v %#v\n", s, s1)
}

But go vet complains:

test.go:12: database/sql.NullInt64 composite literal uses unkeyed fields

Question is: why it does complain on line 12 and does not complain on line 13 here ?

Ainar-G · Accepted Answer · 2014-12-20 10:23:37Z

3

It's asking you to add the keys, e.g.

var s = sql.NullInt64{Int64: 1, Valid: true}

answered Dec 20, 2014 at 10:23

Ainar-G

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2 Comments

Dfr Over a year ago

Yes, but other structs with 1-2 elements i used to initialize without keys and just wondering what is different about this type, why it suddenly needs explicit keys

Mr_Pink Over a year ago

@Dfr: It doesn't need keys. go vet is suggesting that you use them to prevent possible errors (like renaming or reordering of the struct fields).

lunixbochs · Accepted Answer · 2014-12-23 08:40:24Z

1

To understand this behavior, we can simply look at the source for go vet in the go.tools repository.

In composite.go:46, it checks the type of the composite literal. If the literal is part of the current package, go vet does not warn you about unkeyed values.

// A simple type name like t or T does not need keys either,
// since it is almost certainly declared in the current package

This check likely exists because an external package could change the struct fields and break your code. Keyed fields make this less of a problem.

answered Dec 23, 2014 at 8:40

lunixbochs

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