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proposal: time: add time.Same, time.Past and time.Future const or enum for time.Compare #57177

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Delta456 opened this issue Dec 8, 2022 · 4 comments
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proposal: time: add time.Same, time.Past and time.Future const or enum for time.Compare #57177

Delta456 opened this issue Dec 8, 2022 · 4 comments
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@Delta456
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Delta456 commented Dec 8, 2022

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")
	}
}
@seankhliao seankhliao changed the title time: add time.Same, time.Past and time.Future const or enum for time.Compare proposal: time: add time.Same, time.Past and time.Future const or enum for time.Compare Dec 8, 2022
@gopherbot gopherbot added this to the Proposal milestone Dec 8, 2022
@dsnet
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dsnet commented Dec 8, 2022

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
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icholy commented Dec 8, 2022

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
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dsnet commented Dec 8, 2022 •
edited
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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

@ianlancetaylor ianlancetaylor moved this to Incoming in Proposals Dec 9, 2022
@Delta456
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Delta456 commented Dec 9, 2022

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.

@Delta456 Delta456 closed this as completed Dec 9, 2022
@golang golang locked and limited conversation to collaborators Dec 9, 2023
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@icholy @dsnet @gopherbot @Delta456