proposal: spec: support struct constant

[huykingsofm]

Go Programming Experience

Experienced

Other Languages Experience

Go, C++

Related Idea

• Has this idea, or one like it, been proposed before?
• Does this affect error handling?
• Is this about generics?
• Is this change backward compatible? Breaking the Go 1 compatibility guarantee is a large cost and requires a large benefit

Has this idea, or one like it, been proposed before?

No

Does this affect error handling?

No

Is this about generics?

No

Proposal

type RGBColor struct {
    r int
    g int
    b int
}

var (
    Red    = RGBColor{r: 255, g: 0, b: 0}   // Pure red
    Green  = RGBColor{r: 0, g: 255, b: 0}   // Pure green
    Blue   = RGBColor{r: 0, g: 0, b: 255}   // Pure blue
    Yellow = RGBColor{r: 255, g: 255, b: 0} // Pure yellow
)

Why can't the above colors be constants?

Language Spec Changes

Go should allow defining a struct constant like

const Red = RGBColor{r: 255, g: 0, b: 0}

For defining unexported structs or structs with unexported fields, Go also should support a constant function like:

constfunc NewConstRGBColor(r, g, b int) RGBColor {
    return RGBColor{r: r, g: g, b: b}
}

Informal Change

No response

Is this change backward compatible?

Yes

Orthogonality: How does this change interact or overlap with existing features?

No response

Would this change make Go easier or harder to learn, and why?

No response

Cost Description

No response

Changes to Go ToolChain

No response

Performance Costs

No response

Prototype

No response

[gabyhelp]

Related Issues

• proposal: allow constants in struct tags #50463 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[seankhliao]

Duplicate of #6386