proposal: pointer: new package for pointer allocation and dereference

[matthinrichsen-wf]

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
}

2. 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.

3. 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
}

[seankhliao]

we just declined #61082

[matthinrichsen-wf]

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

[adonovan]

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]

@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]

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

[rsc]

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