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proposal: spec: user-defined map keys #283

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gopherbot opened this issue Nov 20, 2009 · 9 comments
Closed

proposal: spec: user-defined map keys #283

gopherbot opened this issue Nov 20, 2009 · 9 comments
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FrozenDueToAge LanguageChange Suggested changes to the Go language v2 An incompatible library change
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Unplanned

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@gopherbot
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by jbamsterdam:

The valid types for map keys are limited. User-defined types that meet the 
appropriate criteria (e.g. having Hash and Equals functions) should be 
permitted.

Alternatively, consider a library package that exposes the internal map 
implementation in a general way.
@robpike
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robpike commented Nov 20, 2009

Comment 1:

Status changed to LongTerm.

@rsc
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rsc commented Dec 2, 2009

Comment 2:

Labels changed: added languagechange.

@rsc
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rsc commented Dec 9, 2011

Comment 4:

Labels changed: added priority-later.

@rsc
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rsc commented Jan 29, 2012

Comment 5:

You can use structs as map keys now.

Labels changed: added priority-someday, removed priority-later.

@rsc
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rsc commented Dec 4, 2013

Comment 6:

Labels changed: added repo-main.

@rsc
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rsc commented Mar 3, 2014

Comment 7:

Adding Release=None to all Priority=Someday bugs.

Labels changed: added release-none.

@gopherbot gopherbot added longterm LanguageChange Suggested changes to the Go language labels Mar 3, 2014
@rsc
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rsc commented Apr 10, 2015

Moving priority-someday to the Unplanned milestone.

@rsc rsc added this to the Unplanned milestone Apr 10, 2015
Arista-Jenkins pushed a commit to aristanetworks/goarista that referenced this issue May 2, 2016
@tsuna
key: Make map[Key]interface{} always O(1) with some runtime hacks.
59d8141 
This is based on a POC from Frank Somers.
This is a workaround for golang/go#283.

Before:
BenchmarkBigMapWithCompositeKeys-8      2000   2863709 ns/op

After:
BenchmarkBigMapWithCompositeKeys-8  10000000       573 ns/op

Unsurprisingly, the O(N) implementation is super slow with a map size of
10000 entries, compared to the O(1) implementation.

Change-Id: Ia9ed056218c59e77b64aceb59e23b95d37760e85
@tv42
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tv42 commented Jul 28, 2016 •
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You could maybe use https://tip.golang.org/pkg/reflect/#StructOf instead of a map, to make compound keys with arbitrary components.

@rsc rsc changed the title ponies: user-defined map keys proposal: spec: user-defined map keys Jun 20, 2017
@rsc rsc added the v2 An incompatible library change label Jun 20, 2017
@ianlancetaylor
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I'm going to close this. If we had generics (#15292) that would be a better approach to this. Or, write your own wrapper functions that use a map[uint64][]T and write a hash function from T to uint64 and code that uses your equals function on each element in the slice. Or something like that. Anyhow, we aren't going to add this particular case to the language itself, except via generics.

@dsnet dsnet mentioned this issue Mar 1, 2018
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@rsc @tv42 @ianlancetaylor @robpike @gopherbot