Annotation

Annotation is a go package that allows parsing and read Java Style annotation strings e.x @SomeAnnotation(param="value"), this package is used by go-service to read and parse annotations in comments.

Install

Using go get

go get -u github.com/go-services/annotation

If you are using dep

dep ensure --add github.com/go-services/annotation

Usage

The package can only be used for string that only contain the annotation, it can not find the annotation in an arbitrary string.

Example

package main

import (
	"github.com/go-services/annotation"
	"fmt"
)

func main() {
	annotationString := `@Annotation(
                            stringParam='String Value',
                            someInt=2,
                            someBool=true,
                            someFloat=2.5
                        )`
	ann, _ := annotation.Parse(annotationString)
	fmt.Printf("Annotation Name: %s\n", ann.Name)                                // Annotation Name: Annotation
	fmt.Printf("Annotation stringParam = %s\n", ann.Get("stringParam").String()) // Annotation stringParam = String Value
	fmt.Printf("Annotation someInt = %d\n", ann.Get("someInt").Int())            // Annotation someInt = 2
	fmt.Printf("Annotation someBool = %t\n", ann.Get("someBool").Bool())         // Annotation someBool = true
	fmt.Printf("Annotation someFloat = %.4f\n", ann.Get("someFloat").Float())    // Annotation someInt = 2.5000
}

Definitions

Annotation also provides a way to check if the annotation has the correct parameters, name.

ParameterDefinition

type ParameterDefinition struct {
	// name the parameter name
	name     string
	
	// required tells if the parameter is required
	required bool
	
	// tp shows the required type of the annotation
	tp       ValueType
}

Definition

// Definition describes the Annotation definition.
type Definition struct {
	// Name is the Name of the Annotation e.x Hello for // @Hello().
	name string

	// should the definition allow unknown parameters
	allowUnknownParameters bool

	// parameters has a list of parameter definitions
	parameters []ParameterDefinition
}

Example

package main

import (
	"github.com/go-services/annotation"
	"fmt"
)

func main() {
    annotationString := `@Annotation(
                        stringParam='String Value',
                        someInt=2,
                        someBool=true,
                        someFloat=2.5
                    )`
	ann, _ := annotation.Parse(annotationString)
	stringParam := annotation.NewParameterDefinition("stringParam", true, annotation.STRING)
	someInt := annotation.NewParameterDefinition("someInt", true, annotation.INT)
	someBool := annotation.NewParameterDefinition("someBool", true, annotation.BOOL)
	someFloat := annotation.NewParameterDefinition("someFloat", true, annotation.FLOAT)
	definition := annotation.NewDefinition(
		"Annotation",
		false,
		stringParam,
		someInt,
		someBool,
		someFloat,
	)
	err := definition.Check(*ann)

	fmt.Println(err) // <nil>

	annotationMissingParam := "@Annotation(someInt=2, someBool=true, someFloat=2.5)"
	annWrong, _ := annotation.Parse(annotationMissingParam)
	err = definition.Check(*annWrong)
	fmt.Println(err) // the `stringParam` parameter is required for @Annotation() Annotation

}