tag

README

tag

DEPRECATED: This project has been moved to github.com/quartercastle/structtag

The motivation behind this package is that the StructTag implementation shipped with Go's standard library is very limited in detecting a malformed StructTag and each time StructTag.Get(key) gets called, it results in the StructTag being parsed again. Another problem is that the StructTag can not be easily manipulated because it is basically a string. This package provides a way to parse the StructTag into a Tag map. This allows fast lookups and easy manipulation of the key value pairs within the Tag.

// Example of struct using tags to append metadata to fields.
type Server struct {
	Host string `json:"host" env:"SERVER_HOST" default:"localhost"`
	Port int    `json:"port" env:"SERVER_PORT" default:"3000"`
}

Install

go get github.com/kvartborg/tag

Usage

t, err := tag.Parse(`json:"host" env:"SERVER_HOST"`)

if err != nil {
  panic(err)
}

fmt.Println(t["json"])

See godoc for full documentation.

License

This project is licensed under the MIT License.

Documentation

Overview

The motivation behind this package is that the StructTag implementation shipped with Go's standard library is very limited in detecting a malformed StructTag and each time StructTag.Get(key) gets called, it results in the StructTag being parsed again. Another problem is that the StructTag can not be easily manipulated because it is basically a string. This package provides a way to parse the StructTag into a Tag map, which allows for fast lookups and easy manipulation of key value pairs within the Tag.

Deprecated: This package has been moved to github.com/quartercastle/structtag

// Example of struct using tags to append metadata to fields.
type Server struct {
	Host string `json:"host" env:"SERVER_HOST" default:"localhost"`
	Port int    `json:"port" env:"SERVER_PORT" default:"3000"`
}

Example

package main

import (
	"fmt"

	"github.com/quartercastle/tag"
)

func main() {
	t, err := tag.Parse(`json:"host" env:"SERVER_HOST" default:"localhost"`)

	if err != nil {
		panic(err)
	}

	fmt.Println(t["env"])
}

Output:
SERVER_HOST

Index

• Variables
• type Tag
  • func Merge(tags ...Tag) Tag
  • func Parse(st reflect.StructTag) (Tag, error)
  • func (t Tag) StructTag() reflect.StructTag

Examples

• Package
• Merge
• Parse
• Tag.StructTag

Variables

var (
	// ErrInvalidSyntax is returned when the StructTag syntax is invalid.
	ErrInvalidSyntax = errors.New("invalid syntax for key value pair")

	// ErrInvalidKey is returned if a key is containing invalid characters or
	// is missing.
	ErrInvalidKey = errors.New("invalid key")

	// ErrInvalidValue is returned if a value is not qouted.
	ErrInvalidValue = errors.New("invalid value")

	// ErrInvalidSeparator is returned if comma is used as separator.
	ErrInvalidSeparator = errors.New("invalid separator, key value pairs should be separated by spaces")
)

Types

type Tag

type Tag map[string]string

Tag is just a map of key value pairs.

func Merge

func Merge(tags ...Tag) Tag

Merge multiple tags together into a single Tag. In case of duplicate keys, the last encountered key will overwrite the existing.

Example

package main

import (
	"fmt"

	"github.com/quartercastle/tag"
)

func main() {
	t1 := tag.Tag{
		"env": "TESTING",
	}

	t2 := tag.Tag{
		"env": "HELLO",
	}

	t := tag.Merge(t1, t2)
	fmt.Println(t)
}

Output:
map[env:HELLO]

func Parse

func Parse(st reflect.StructTag) (Tag, error)

Parse takes a StructTag and parses it into a Tag or returns an error. If the given string contains duplicate keys the last key value pair will overwrite the previous.

The parsing logic is a slightly modified version of the StructTag.Lookup function from the reflect package included in the standard library. https://github.com/golang/go/blob/0377f061687771eddfe8de78d6c40e17d6b21a39/src/reflect/type.go#L1132

Example

package main

import (
	"fmt"

	"github.com/quartercastle/tag"
)

func main() {
	t, err := tag.Parse(`env:"SERVER_HOST" default:"localhost"`)
	fmt.Println(t, err)
}

Output:
map[default:localhost env:SERVER_HOST] <nil>

func (Tag) StructTag

func (t Tag) StructTag() reflect.StructTag

StructTag converts the Tag into a StructTag.

Example

package main

import (
	"fmt"

	"github.com/quartercastle/tag"
)

func main() {
	t, _ := tag.Parse(`env:"SERVER_HOST"`)
	st := t.StructTag()
	fmt.Println(st)
}

Output:
env:"SERVER_HOST"