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Table add missing sink #24721

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arnetheduck opened this issue Feb 25, 2025 · 8 comments · Fixed by #24724
Closed

Table add missing sink #24721

arnetheduck opened this issue Feb 25, 2025 · 8 comments · Fixed by #24724
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@ringabout

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@arnetheduck
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Description

Table should not need to copy its key argument during insertion:

import std/tables
type NoCopies = object

proc `=copy`(a: var NoCopies, b: NoCopies) {.error.}

var t: Table[NoCopies, NoCopies]
t[NoCopies()] = NoCopies() # only moves

The same probably holds for a lot of std lib containers, ie the concept applies to all of them.

Nim Version

2.2

Current Output

Error: '=copy' is not available for type <NoCopies>; requires a copy because it's not the last read of 'key'; try to make key a 'sink' parameter; routine: rawInsert

Expected Output

Known Workarounds

No response

Additional Information

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@Araq
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Araq commented Feb 25, 2025

Ping @demotomohiro please work on this.

@ringabout
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I will take over it since it is similar to #24720 which lacks corresponding lent and sink in the stdlibs

@ringabout ringabout self-assigned this Feb 25, 2025
ringabout added a commit that referenced this issue Feb 25, 2025
@ringabout
fixes #24721; Table add missing sink
86688cb
ringabout added a commit that referenced this issue Feb 25, 2025
@ringabout
fixes #24721; Table add missing sink
4c1c06c
@ringabout ringabout mentioned this issue Feb 25, 2025
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@arnetheduck
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Same for toTable

@arnetheduck
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import std/tables
type NoCopies = object

proc `=copy`(a: var NoCopies, b: NoCopies) {.error.}

var t = {NoCopies(): NoCopies()}.toTable()

@ringabout
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ringabout commented Mar 13, 2025 •
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toTable accepts openArray, which is not to be sunk. Because openArray, which is a view type, doesn't own data. But sink requires owning the data so it can destroy the data there. I'm not sure whether to make it work or detect it at the compile time

@ringabout ringabout mentioned this issue Mar 14, 2025
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@arnetheduck
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I'm not sure whether to make it work or detect it at the compile time

well, something like openArray[sinkable[T]] would be the way things happen in other languages - ie the openArray should "pass on" the sinkability of its members so that {$1: $2}.toTable can move the two allocated strings into table storage.

@beef331
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beef331 commented Mar 14, 2025 •
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It could be a breaking change but adding specializations on seq and array would make it sinkable.

@arnetheduck
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adding specializations

this makes for a messy language because every time there's something that takes openArray, it would also need these specializations which kind of defeats one of the purposes of openArray..

Araq pushed a commit that referenced this issue Mar 22, 2025
@ringabout
fixes #24721; Table add missing sink (#24724)
482662d 
fixes #24721
narimiran pushed a commit that referenced this issue Mar 25, 2025
@ringabout @narimiran
fixes #24721; Table add missing sink (#24724)
20362cc 
fixes #24721

(cherry picked from commit 482662d)
narimiran added a commit that referenced this issue Mar 25, 2025
@narimiran
Revert "fixes #24721; Table add missing sink (#24724)"
5c9aea9 
This reverts commit 20362cc.
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fixes #24721; Table add missing sink nim-lang/Nim
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@Araq @arnetheduck @beef331 @ringabout