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proposal: Go 2: allow interface pointer receivers #31146

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zigazeljko opened this issue Mar 29, 2019 · 3 comments
Closed

proposal: Go 2: allow interface pointer receivers #31146

zigazeljko opened this issue Mar 29, 2019 · 3 comments
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FrozenDueToAge LanguageChange Proposal v2 A language change or incompatible library change
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Proposal

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@zigazeljko
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What version of Go are you using (go version)?

$ go version
go version go1.11 linux/amd64

Currently, methods are not allowed to have an interface receiver or an interface pointer receiver. While methods with interface (value) receivers are clearly not possible, methods with interface pointer receivers (and consequently having interface pointers implement other interfaces) should be possible. This would be extremly useful for cases such as unmarshaling polymorphic JSON.

For example:

type MyInterface {
    ...
}

func (p *MyInterface) UnmarshalJSON(data []byte) error {
    *p = ...
}

var obj MyInterface
json.Unmarshal(data, &obj)
// &obj implements json.Unmarshaler
@gopherbot gopherbot added this to the Proposal milestone Mar 29, 2019
@ianlancetaylor ianlancetaylor changed the title proposal: spec: allow interface pointer receivers proposal: Go 2: allow interface pointer receivers Mar 29, 2019
@ianlancetaylor ianlancetaylor added LanguageChange v2 A language change or incompatible library change labels Mar 29, 2019
@ianlancetaylor
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What if you write

type MyInterfaceWrapper struct {
    wrapping MyInterface
}

func (p *MyInterfaceWrapper) UnmarshalJSON(data []byte) error { ... }

var obj MyInterfaceWrapper
json.Unmarshal(&obj)
// pull out value from wrapping field

Just to clarify what you are proposing, is there anything this proposal permits that we couldn't do with an approach like that?

@zigazeljko
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@ianlancetaylor I think not (apart from simplifying code in such cases).

@ianlancetaylor
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Thanks, but since this proposal would make the relationship between interfaces and methods more confusing, and since it would not add functionality that we can't already get in other ways, we aren't going to move this forward with this proposal.

@golang golang locked and limited conversation to collaborators May 6, 2020
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FrozenDueToAge LanguageChange Proposal v2 A language change or incompatible library change
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@zigazeljko @ianlancetaylor @gopherbot