What is the namespace of variables inside html/text
templates? I thought that a variable $x
can change value inside a template, but this example shows me that I cannot.
I failed when I tried to group tournaments according year - something like this (http://play.golang.org/p/EX1Aut_ULD):
package main
import (
"fmt"
"os"
"text/template"
"time"
)
func main() {
tournaments := []struct {
Place string
Date time.Time
}{
// for clarity - date is sorted, we don't need sort it again
{"Town1", time.Date(2015, time.November, 10, 23, 0, 0, 0, time.Local)},
{"Town2", time.Date(2015, time.October, 10, 23, 0, 0, 0, time.Local)},
{"Town3", time.Date(2014, time.November, 10, 23, 0, 0, 0, time.Local)},
}
t, err := template.New("").Parse(`
{{$prev_year:=0}}
{{range .}}
{{with .Date}}
{{$year:=.Year}}
{{if ne $year $prev_year}}
Actions in year {{$year}}:
{{$prev_year:=$year}}
{{end}}
{{end}}
{{.Place}}, {{.Date}}
{{end}}
`)
if err != nil {
panic(err)
}
err = t.Execute(os.Stdout, tournaments)
if err != nil {
fmt.Println("executing template:", err)
}
}
Edit: See https://stackoverflow.com/a/52925780/1685538 for a more up-to-date answer.
Original answer:
https://golang.org/pkg/text/template/#hdr-Variables:
A variable's scope extends to the "end" action of the control structure ("if", "with", or "range") in which it is declared, or to the end of the template if there is no such control structure.
So the $prev_year
you define with {{$prev_year:=$year}}
only lives until.. the next line ({{end}}
).
It seems there is no way of going around that.
The "right" way to do this is to take that logic out of your template, and do the grouping in your Go code.
Here is a working example : https://play.golang.org/p/DZoSXo9WQR
package main
import (
"fmt"
"os"
"text/template"
"time"
)
type Tournament struct {
Place string
Date time.Time
}
type TournamentGroup struct {
Year int
Tournaments []Tournament
}
func groupTournamentsByYear(tournaments []Tournament) []TournamentGroup {
if len(tournaments) == 0 {
return nil
}
result := []TournamentGroup{
{
Year: tournaments[0].Date.Year(),
Tournaments: make([]Tournament, 0, 1),
},
}
i := 0
for _, tournament := range tournaments {
year := tournament.Date.Year()
if result[i].Year == year {
// Add to existing group
result[i].Tournaments = append(result[i].Tournaments, tournament)
} else {
// New group
result = append(result, TournamentGroup{
Year: year,
Tournaments: []Tournament{
tournament,
},
})
i++
}
}
return result
}
func main() {
tournaments := []Tournament{
// for clarity - date is sorted, we don't need sort it again
{"Town1", time.Date(2015, time.November, 10, 23, 0, 0, 0, time.Local)},
{"Town2", time.Date(2015, time.October, 10, 23, 0, 0, 0, time.Local)},
{"Town3", time.Date(2014, time.November, 10, 23, 0, 0, 0, time.Local)},
}
t, err := template.New("").Parse(`
{{$prev_year:=0}}
{{range .}}
Actions in year {{.Year}}:
{{range .Tournaments}}
{{.Place}}, {{.Date}}
{{end}}
{{end}}
`)
if err != nil {
panic(err)
}
err = t.Execute(os.Stdout, groupTournamentsByYear(tournaments))
if err != nil {
fmt.Println("executing template:", err)
}
}