Go Template Function Operations

The goal of this library is to quickly add some reflection based functional functions to the text/template and html/template language. Namely:

• map
• filter
• find
• findIndex

This library exists in lieu of generic support in text/template or html/template.

Exported functions:

• func MapTemplateFunc(slice any, f any) (any, error) The map function.
• func FilterTemplateFunc(slice any, f any) (any, error) The map function.
• func TextFunctions() text/template.FuncMap
• func HtmlFunctions() html/template.FuncMap

Template Function definitions

interface.go:

func TextFunctions() tt.FuncMap {
	return map[string]any{
		"filter":    FilterTemplateFunc,
		"find":      FindTemplateFunc,
		"findIndex": FindIndexTemplateFunc,
		"map":       MapTemplateFunc,
	}
}

func HtmlFunctions() ht.FuncMap {
	return map[string]any{
		"filter":    FilterTemplateFunc,
		"find":      FindTemplateFunc,
		"findIndex": FindIndexTemplateFunc,
		"map":       MapTemplateFunc,
	}
}

map

In go: MapTemplateFunc, provided as map by TextFunctions and HtmlFunctions

Definition:

func MapTemplateFunc(slice any, f any) (any, error)

• The first argument slice must be a slice (or nil), of any type.
• Second argument f must be a function of these definitions:
  • func () any
  • func () (any, error)
  • func (v any) any
  • func (v any) (any, error)

The return will be:

• The first result: an array of the same length as slice in the case, or nil if there was an error. The output of f will be in the appropriate place for each value
• The 2nd result: an error if there was an error: See errors.go for a complete list.

Usage:

• {{ map $.Data $.Funcs.inc }}
• {{ map $.Data $.Funcs.odd }}

filter

In go: FilterTemplateFunc, provided as filter by TextFunctions and HtmlFunctions

Definition:

func FilterTemplateFunc(slice any, f any) (any, error)

• The first argument slice must be a slice (or nil), of any type.
• Second argument f must be a function of these definitions:
  • func () bool
  • func () (bool, error)
  • func (v any) bool
  • func (v any) (bool, error)

The return will be:

• The first result: an array of the same length or smaller as slice in the case, or nil if there was an error. The output of f will be a slice which only contains the values which f returned true for slice
• The 2nd result: an error if there was an error: See errors.go for a complete list.

Usage:

• {{ filter $.Data $.Funcs.odd }}

find

In go: FindTemplateFunc, provided as find by TextFunctions and HtmlFunctions

Definition:

func FindTemplateFunc(slice any, f any) (any, error)

• The first argument slice must be a slice (or nil), of any type.
• Second argument f must be a function of these definitions:
  • func () bool
  • func () (bool, error)
  • func (v any) bool
  • func (v any) (bool, error)

The return will be:

• The first matching value, or nil
• The 2nd result: an error if there was an error: See errors.go for a complete list.

Usage:

• {{ filter $.Data $.Funcs.odd }}

findIndex

In go: FindIndexTemplateFunc, provided as findIndex by TextFunctions and HtmlFunctions

Definition:

func FindIndexTemplateFunc(slice any, f any) (int, error)

• The first argument slice must be a slice (or nil), of any type.
• Second argument f must be a function of these definitions:
  • func () bool
  • func () (bool, error)
  • func (v any) bool
  • func (v any) (bool, error)

The return will be:

• The first matching index, or -1
• The 2nd result: an error if there was an error: See errors.go for a complete list.

Usage:

• {{ filter $.Data $.Funcs.odd }}

Usage:

package main

import (
	"fmt"
	"github.com/arran4/go-template-functional-operations"
	"github.com/arran4/go-template-functional-operations/misc"
	"os"
	"text/template"
)

func main() {
	funcs := map[string]any{
		"inc": func(i int) int {
			return i + 1
		},
		"odd": func(i int) bool {
			return i%2 == 1
		},
	}
	funcs = misc.MergeMaps(funtemplates.TextFunctions(), funcs)

	tmpl := template.Must(template.New("").Funcs(funcs).Parse(`
        {{ map $.Data $.Funcs.inc }}
        {{ map $.Data $.Funcs.odd }}
    `))

	data := struct {
		Data  []int
		Funcs map[string]any
	}{
		Data:  []int{1, 2, 3, 4},
		Funcs: funcs,
	}

	err := tmpl.Execute(os.Stdout, data)
	if err != nil {
		fmt.Println(err)
	}
}

Returns:

        [2 3 4 5]
        [true false true false]