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proposal: pointer: new package for pointer allocation and dereference #64749

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matthinrichsen-wf opened this issue Dec 15, 2023 · 6 comments
Closed

proposal: pointer: new package for pointer allocation and dereference #64749

matthinrichsen-wf opened this issue Dec 15, 2023 · 6 comments
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@matthinrichsen-wf
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matthinrichsen-wf commented Dec 15, 2023 •
edited

Proposal Details

A project I'm working on currently makes heavy use of utilities that:

  1. Safely Dereference a pointer:

ex 1.

func ToValue[T any](p *T) (T, bool) {
   if p == nil {
       var t T
       return t, false
   }
   return *p, true
}

ex 2.

func ToValueWithNil[T any](p *T, valueIfNil T) T {
   if p == nil {
       return valueIfNil
   }
   return *p
}
  1. Generically Convert a Value to a Pointer:

ex.

func FromValue[T any](value T) *T {
 return &value
}

It would be nice to have utilities like these in the standard library as they seem generally useful.

  1. Compare Pointers and Their Values:

ex.

func ValuesEqual[T comparable](p1, p2 *T) bool {
  if p1 == nil || p2 == nil {
     return p1 == p2
  }
  return *p1 == *p2
}
@gopherbot gopherbot added this to the Proposal milestone Dec 15, 2023
@seankhliao
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we just declined #61082

@matthinrichsen-wf
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@seankhliao I see. I searched for prior art, but must not have looked at closed proposals.

@seankhliao seankhliao changed the title proposal: "pointer": Generic Pointer Utilities proposal: "pointer": pointer value wrapping / unwrapping Dec 17, 2023
@adonovan
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These functions seem easy enough to define in the relatively few places where they are heavily needed.

Also, ToValueWithNil is strict in both arguments, whereas the more useful semantics (in my experience) are lazy: ptr ? *ptr : computeDefault() in C conditional notation.

@matthinrichsen-wf
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matthinrichsen-wf commented Dec 20, 2023 •
edited

@adonovan Fair points.

As far as ToValue* are concerned, I think they would be obviated by a safe-deference (like we have for safe map accesses):

value, ok := *somePointer
if !ok {
    value = someValueIfNil
}

(which I would also love to have instead tbh)

@rsc
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rsc commented Jan 10, 2024

These don't meet the bar for the standard library.

@rsc rsc changed the title proposal: "pointer": pointer value wrapping / unwrapping proposal: pointer: new package for pointer allocation and dereference Jan 10, 2024
@rsc
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rsc commented Jan 10, 2024

No change in consensus, so declined.
— rsc for the proposal review group

@rsc rsc closed this as completed Jan 10, 2024
@AlekSi AlekSi mentioned this issue Jan 12, 2024
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@seankhliao seankhliao mentioned this issue Mar 15, 2024
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@rsc @adonovan @matthinrichsen-wf @gopherbot @seankhliao