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fmt: refers to the empty interface by the longer, older "interface {}" name instead of the shorter, newer "any" #65912

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dmitshur opened this issue Feb 23, 2024 · 5 comments
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fmt: refers to the empty interface by the longer, older "interface {}" name instead of the shorter, newer "any" #65912

dmitshur opened this issue Feb 23, 2024 · 5 comments
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FeatureRequest Issues asking for a new feature that does not need a proposal. FrozenDueToAge NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.
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@dmitshur
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dmitshur commented Feb 23, 2024 •
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Go version

go version go1.22.0 darwin/arm64

Output of go env in your module/workspace:

N/A

What did you do?

I used fmt's %#v to print a value whose type involves the empty interface in a module that declares Go version 1.22.0.

fmt.Printf("value of []any{1, 2} is %#v\n", []any{1, 2})

https://go.dev/play/p/pByHBo9Vs03

What did you see happen?

value of []any{1, 2} is []interface {}{1, 2}

What did you expect to see?

Go 1.18 added the predeclared type any as an alias for the empty interface.

It might be an enhancement if fmt were to take advantage of it, and print:

value of []any{1, 2} is []any{1, 2}

CC @robpike, @martisch.
@dmitshur dmitshur added FeatureRequest Issues asking for a new feature that does not need a proposal. NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels Feb 23, 2024
@dmitshur dmitshur added this to the Backlog milestone Feb 23, 2024
@cherrymui
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any is defined as an alias to interface{}. We print the byte type as the unaliased uint8, so we probably should print any as the unaliased interface{} as well.

@cherrymui
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Well, for byte, when printing the type (%T) it prints uint8, but when printing value (%#v) it prints byte. For rune we print int32 for both. https://go.dev/play/p/yttrKyuyZrP . That seems inconsistent.

@zigo101
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zigo101 commented Feb 23, 2024

See #44391 and #14830.

@robpike
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robpike commented Feb 23, 2024

I wouldn't change this. It's clear and also has the potential to break a lot of golden files.

@dmitshur
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It sounds like this is okay to leave as is then. If in the future this change (possibly bundled with others like it) gets a higher benefit-to-cost ratio, a new issue can be filed (referencing this one). Thanks for considering it.

@dmitshur dmitshur closed this as not planned Won't fix, can't repro, duplicate, stale Feb 23, 2024
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