proposal: time: add time.Equal and time.Compare

[andig]

Proposal Details

Observation

I've just found myself writing this code working with timestamps:

if !slices.ContainsFunc(keys, func(ts time.Time) bool {
	return ts.Equal(r.Start)
}) {
	keys = append(keys, r.Start)
}

keys = slices.SortedFunc(slices.Values(keys), func(a, b time.Time) int {
	return a.Compare(b)
})

While this is a perfectly valid way of doing things it felt odd the I couldn't simply do

slices.ContainsFunc(keys, time.Equal)
slices.SortedFunc(slices.Values(keys), time.Compare)

Proposal

Especially the comparison takes careful consideration of order (i.e. how to compare). For simplicity, I propose adding

func Equal(a, b Time) bool {
	return a.Equal(b)
}

func Compare(a, b Time) int {
	return a.Compare(b)
}

While Go strives to have only one way of doing things there are other examples of comfort functions like e.g. UnixMilli, UnixMicro that are not strictly necessary.

Alternatives

1. I thought about using cmp.Compare but cmp.Ordered this does not cover time.Time. At least as far as time.Compare goes this would be a great alternative. A cmp.Equal might complement that.

2. Another potential pattern might be to introduce general Equal and Compare interfaces and a matching adapter function:

   interface Equal[T any] {
       Equal(to T) bool
   }
   
   func Equal[T Equal]() func(a, b T) bool {
       return a.Equal(b)
   }
   
   // usage (not sure if the type could be inferred)
   slices.ContainsFunc(keys, Equal[time.Time]())
   
   interface Comparable[T any] {
       Compare(with T) int
   }
   
   func Compare[T Comparable]() func(a, b T) int {
       return a.Compare(b)
   }
   
   // usage (not sure if the type could be inferred)
   slices.SortedFunc(slices.Values(keys), Compare[time.Time]())

[gabyhelp]

Related Issues

• proposal: time: add Compare #62642 (closed)
• time: add Time.Compare #50770 (closed)
• proposal: time: add time.Same, time.Past and time.Future const or enum for time.Compare #57177 (closed)
• proposal: cmd/vet: time.Time should not compared #45961 (closed)
• Add BeforeOrEqual and AfterOrEqual methods to the time.Time struct #33511 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[ianlancetaylor]

Note that you can already write

    if !slices.ContainsFunc(keys, r.Start.Equal) { ... }

[andig]

Thank you. Should have thought of this. It's similar to using time.Time.Compare but less astonishing. Need to ask about the latter in golang nuts (I did: https://groups.google.com/g/golang-nuts/c/SmW-9cg3T1A).