proposal: time: add time.Same, time.Past and time.Future const or enum for time.Compare

[Delta456]

From commit, I think we should be using an enum or const for the return type of time.Compare instead of hardcoded values. It makes the code easier to understand and maintain. This can be seen below:

// src/time/time.go
package time

const (
  Same = 0
  Past = +1
  Furue = -1
)

// ...

Example code:

package main

import (
	"fmt"
	"time"
)

func main() {
	var (
		t1 = time.Now()
		t2 = t1.Add(time.Hour)
	)
	switch t1.Compare(t2) {
	case time.Same:
		fmt.Println("same")
	case time.Past:
		fmt.Println("past")
	case time.Future:
		fmt.Println("future")
	}
}

[dsnet]

The -1, 0, +1 convention is relatively common:

• bytes.Compare
• subtle.ConstantTimeCompare
• netip.Addr.Compare

I don't think we want to set the precedence that each of these should be accompanied by a constant.

[icholy]

For me, the problem is remembering how they're being compared. Example:

if t1.Compare(t2) == time.Future {
    // is it t1 or t2 that's in the future?
}

[dsnet]

The mnemonic I use to remember Compare like operations is that:

t1.Compare(t2) < 0 // is equivalent to t1 < t2
t1.Compare(t2) > 0 // is equivalent to t1 > t2

Essentially, you replace the Compare with the < or > operator that is just to the right of it.

Similarly:

t1.Compare(t2) <= 0 // is equivalent to t1 <= t2
t1.Compare(t2) >= 0 // is equivalent to t1 >= t2
t1.Compare(t2) == 0 // is equivalent to t1 == t2

[Delta456]

The mnemonic I use to remember Compare like operations is that:

t1.Compare(t2) < 0 // is equivalent to t1 < t2
t1.Compare(t2) > 0 // is equivalent to t1 > t2

Essentially, you replace the Compare with the < or > operator that is just to the right of it.

Similarly:

t1.Compare(t2) <= 0 // is equivalent to t1 <= t2
t1.Compare(t2) >= 0 // is equivalent to t1 >= t2
t1.Compare(t2) == 0 // is equivalent to t1 == t2

Oh, I see. I think the current way matches the semantics of bytes.Compare, subtle.ConstantTimeCompare, netip.Addr.Compare so this proposal can be closed.