Help with if statement

[dugwill]

New to GO. I am working through the Donovan/Kernighan book.

I am trying to compare two time.Time variables in an if statement.

if item.CreatedAt < yearAgo {
…
}

Both var are of type time.Time. “item.CreatedAt” is from a struct and yearAgo is calculated:

t0 := time.Now()
var yearAgo time.Time = t0.Add(-timeCalc.OneYear)

when I build this is get an error:

github.com\dugwill\gopl.io\ch4\issues\main.go:41: invalid operation: item.CreatedAt < yearAgo (operator < not defined on struct)

I would expect this, I think, if I would comparing two structs. I don’t understand why I get it when comparing to vars of the same type.

Code can be found at

github.com/dugwill/gopl.io/blob/Chapter4/ch4/issues/main.go

Regards

[geosoft1 (George Calianu)]

you can compare as Unix time

package main

import(
	"fmt"
	"time"
)

func main(){
t0 := time.Now().Unix()
time.Sleep(time.Second*3)
t1 := time.Now().Unix()
fmt.Println(t1 - t0)
}

Running…

3

Success: process exited with code 0.

[calmh (Jakob Borg)]

Or, perhaps better:

if t0.Before(t1) {
    // true when t0 < t1
}

diff := t0.Sub(t1)
// diff is a time.Duration that you can do stuff with
// ...

[elithrar (Matt Silverlock)]

I would expect this, I think, if I would comparing two structs. I don’t understand why I get it when comparing to vars of the same type.

The “vars” are structs: a variable has a type. time.Time is defined as a struct.

If you want to determine whether a time is before/after another time, you can use time.After (or Before) to do this.

e.g.

package main

import "time"

func main() {
	now := time.Now()
	tomorrow := now.Add(time.Hour * 24)

	if tomorrow.After(now) {
		// Is after!
	} else {
		// is the same instant or before
	}
}

[dugwill]

Thanks for the the help. Lots of options. The time.After/Before is especially elegant. Its goona take me a while to find all the gems in Go.