templates-strings-replace.go

package main

import (
	"fmt"
	"os"
	"strings"
	"text/template"
)

func replace(a, b, c string, n int) string {
	return strings.Replace(a, b, c, n)
}

func main() {
	fmt.Println(strings.Replace("foo", "f", "b", -1))

	// Cannot use arbitrary functions.
	//tmpl := `{{print "xyzzy"}}{{call strings.Replace "foo/bar" "/" "-" 1}}{{print "quux"}}`
	//tmpl := `{{print "xyzzy"}}{{call "strings.Replace" "foo/bar" "/" "-" 1}}{{print "quux"}}`
	//tmpl := `{{print "xyzzy"}}{{call replace "foo/bar" "/" "-" 1}}{{print "quux"}}`
	//tmpl := `{{print "xyzzy"}}{{call "replace" "foo/bar" "/" "-" 1}}{{print "quux"}}`

	// The documentation says we can use functions in "the global function map",
	// but apparently that does not include strings.Replace or the replace
	// function defined above:
	//     During execution functions are found in two function maps: first in the
	//     template, then in the global function map. By default, no functions are
	//     defined in the template but the Funcs method can be used to add them.
	// https://golang.org/pkg/text/template/#hdr-Functions

	// Cannot range over a string.
	//tmpl := `{{range .}}{{print "x"}}{{end}}`

	// Cannot range over a string this way either.
	//tmpl := `{{range $i, $x := .}}{{"x"}}{{end}}`

	// block does not work.
	//tmpl := `{{block "f" .}}{{.}}{{end}}`

	// Cannot use slice expressions with index.
	//tmpl := `{{define "f"}}{{printf "%v" .}}{{end}}{{template "f" index . 1:}}`

	// Cannot do arithmetic ("-" is not recognised as an operator, "add",
	// "subtract", and "minus" are not recognised as functions).
	//tmpl := `{{printf "%.*s" 6 (len . - 1)}}`
	//tmpl := `{{printf "%.*s" 6 (add (len .) -1)}}`
	//tmpl := `{{printf "%.*s" 6 (subtract (len .) -1)}}`
	//tmpl := `{{printf "%.*s" 6 (add (len .) -1)}}`

	// All the information I can find online suggests creating a custom function
	// (which is not an option for me):
	// https://www.reddit.com/r/golang/comments/38g9og/substringing_in_go_templates/
	// http://stackoverflow.com/questions/19771787/golang-how-to-split-string-in-template
	// http://stackoverflow.com/questions/25173549/go-templates-range-over-string
	// http://stackoverflow.com/questions/25689829/arithmetic-in-go-templates

	// Hey, recursion works!
	//tmpl := `{{define "f"}}{{template "f"}}{{end}}{{template "f"}}`

	// Hey, maybe we could do some nasty hack with len and string truncation!
	tmpl := `{{printf "%.*s %v" 6 . (len .)}}`

	// We can catenate strings and call len on them! We could add recursion to
	// this to build up a string $x and terminate when (len $x) equals the length
	// of our input.
	//tmpl := `{{$x := ""}}{{$x := printf "%s%s" $x "x"}}{{printf "%d " (len $x)}}{{$x := printf "%s%s" $x "x"}}{{printf "%d " (len $x)}}{{$x := printf "%s%s" $x "x"}}{{printf "%d " (len $x)}}`

	// Cannot reference a variable defined outside a template from within that
	// template.
	//tmpl := `{{$s := .}}{{$x := ""}}{{$n := len .}}{{define "f"}}{{$x := printf "%s%s" "x" "x"}}{{$i := len $x}}{{printf "%v %v" "blah" $i}}{{end}}{{template "f"}}`

	t, err := template.New("slash-to-dash").Parse(tmpl)
	if err != nil {
		fmt.Printf("template.New(): %v\n", err)
		os.Exit(1)
	}

	t.Execute(os.Stdout, "namespace/name")
	//t.Execute(os.Stdout, []string{"namespace/name"})
}