Go: proposal: spec: require tagged literals for external structs
It would aid compatibility and evolution if a package writer knew that all clients
creating structs with types exported from the package use the form
pkg.Struct{A: a, B: b}
rather than
pkg.Struct{a, b}
It may be worth making this a language restriction
robpike
All 8 comments
rsc
on 12 Sep 2012
rsc
on 3 Mar 2014
At present there is a vet check for this:
> go vet
b.go:5:9: pkg.Struct composite literal uses unkeyed fields
Is there an advantage to promoting this check to the language level?
ianlancetaylor
on 5 Feb 2019
There might be scenarios where it's tedious to have to repeat struct field names over and over again; e.g., for small structs that are frequently created and won't change. Example
p := graphic.Point3D{1, 2, 3}
But for cases like these it's always easy (and probably better) to provide any factory function instead.
griesemer
on 5 Feb 2019
There is a trick to force users of an exported struct to write field names:
type Struct struct {
A int
B string
_ struct{}
}
And for any usage of Struct{1, "2"} a simple compile error will appear:
./prog.go:4:16: too few values in Struct literal (Playground https://play.golang.org/p/sPgtcxAoOxd)
(source: https://groups.google.com/forum/#!topic/golang-nuts/NSjVW82i0mY)
cristaloleg
on 24 Feb 2020
As this is checked by vet today, it does not seem necessary to add to the language proper.
(Perhaps at some future point we should consider promoting some vet checks into the language proper.)
ianlancetaylor
on 17 Mar 2020
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Most helpful comment
There is a trick to force users of an exported struct to write field names:
And for any usage of
Struct{1, "2"}a simple compile error will appear:./prog.go:4:16: too few values in Struct literal(Playground https://play.golang.org/p/sPgtcxAoOxd)(source: https://groups.google.com/forum/#!topic/golang-nuts/NSjVW82i0mY)