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maps: Clarify iteration order of Keys & Values and that Insert overwrites existing keys #67537

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magical opened this issue May 21, 2024 · 4 comments
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maps: Clarify iteration order of Keys & Values and that Insert overwrites existing keys #67537

magical opened this issue May 21, 2024 · 4 comments
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compiler/runtime Issues related to the Go compiler and/or runtime. Documentation Issues describing a change to documentation. NeedsFix The path to resolution is known, but the work has not been done.
Milestone
Go1.23

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@magical
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magical commented May 21, 2024

These functions were added in 2b0f2f8 with minimal documentation.

// Keys returns an iterator over keys in m.
func Keys[Map ~map[K]V, K comparable, V any](m Map) iter.Seq[K] {
	...
}

// Values returns an iterator over values in m.
func Values[Map ~map[K]V, K comparable, V any](m Map) iter.Seq[V] {
	...
}

// Insert adds the key-value pairs from seq to m.
func Insert[Map ~map[K]V, K comparable, V any](m Map, seq iter.Seq2[K, V]) {
	...
}

The doc comments should be updated to specify the iteration order of Keys and Values, and the behaviour of Insert when duplicate keys are inserted, per discussion on #61900 and in particular rsc's comment:

Happy to update docs to say that iteration order is undefined (different each time) and Insert does overwrite keys.
aimuz added a commit to aimuz/go that referenced this issue May 21, 2024
@aimuz
maps: clarify iteration order and insertion behavior
53208a2 
Fixed golang#67537.
@aimuz aimuz mentioned this issue May 21, 2024
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@gopherbot
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Change https://go.dev/cl/587015 mentions this issue: maps: clarify iteration order and insertion behavior

@nightlyone
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What happens when keys are added/removed or values changed while iterating might also be interesting to document.

Maybe it should even all be documented once at a package document and the function document should refer to it

@cagedmantis cagedmantis added compiler/runtime Issues related to the Go compiler and/or runtime. NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels May 21, 2024
@cagedmantis
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cc @ianlancetaylor

@cagedmantis cagedmantis added this to the Go1.23 milestone May 21, 2024
@ianlancetaylor
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I agree that we should document iteration order. I'm not yet convinced we need to document the behavior for concurrent inserts and deletes from the map.

aimuz added a commit to aimuz/go that referenced this issue May 22, 2024
@aimuz
maps: clarify iteration order and insertion behavior
9eec790 
Fixed golang#67537.
@dmitshur dmitshur added Documentation Issues describing a change to documentation. NeedsFix The path to resolution is known, but the work has not been done. and removed NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. labels May 22, 2024
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compiler/runtime Issues related to the Go compiler and/or runtime. Documentation Issues describing a change to documentation. NeedsFix The path to resolution is known, but the work has not been done.
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maps: clarify iteration order and insertion behavior aimuz/go
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@cagedmantis @magical @nightlyone @dmitshur @ianlancetaylor @gopherbot