= Formatters Package Alessandro Sanino [email protected] :source-highlighter: pygments :pygments-style: manni

Formatters is a package which contains a useful and customizable set of formatters for your application.

. Formatter - A generic interface to format data. . TextFormatter - Formats and Prints interface{} to Text String - Binded to String() method. . JSONFormatter - Formats and Prints interface{} to JSON String - Binded to json.Marshal() method.

== Usage [source, go]

type TestType struct { field1 string json:"field1,omitempty" //same json tag as required by json.Marshal field2 int json:"field2" //same json tag as required by json.Marshal }

var a Formatter = TextFormatter{} var b JSONFormatter = JSONFormatter{}

var test TestType{ field1 : "test", field2 : 42, }

var testString = a.Format(test) fmt.Println(testString) // Prints test.String() a.Print(test) // Does the same.

testString = b.Format(test) fmt.Println(testString) // Prints { field1 : "test", field2 : "42" } b.Print(test) // Does the same

=== The default formatter There is a global formatter which can be used across other packages. You can set it with the formatter.setFormatter(Formatter) function. [source, go]

type TestType struct { field1 string json:"field1,omitempty" //same json tag as required by json.Marshal field2 int json:"field2" //same json tag as required by json.Marshal }

var test TestType{ field1 : "test", field2 : 42, }

formatter.setFormatter("text") formatter.Print(test) // Prints string representation of the test struct, using String(). formatter.setFormatter("json") formatter.Print(test) // Prints test struct as a JSON object.

== Custom Formatters It is possible to add custom formatters with the formatter.AddCustomFormatter(format, Formatter) function.

Let's assume we want to add a YamlFormatter which parses to Yaml Objects. [source, go]

// Solution 1 : YamlFormatter is a struct. type YamlFormatter struct{}

func (yf YamlFormatter) Format(msg interface{}) (string, error) { // do something and return values. }

//... formatter.AddCustomFormatter("yaml", YamlFormatter{}) //...

// Solution 2 : YamlFormatter is a int8 or other primitive type, useful for formatters which does not need fields. type YamlFormatter int8

func (yf YamlFormatter) Format(msg interface{}) (string, error) { // do something and return values. }

//... formatter.AddCustomFormatter("yaml", YamlFormatter(3)) // every int8 is valid, this is a cast.

== Printing Errors Just use formatter.PrintErrorMessage(string) or formatter.PrintError(error) function. [source, go]

var errormessage string = "Some error occurred" formatter.PrintErrorMessage(errormessage) // Prints the error formatted properly.

err := functionWhichMayReturnAnError() if err != nil { formatter.PrintError(err) }

== Debug with JSON values JSONFormatter by default does not print what it cannot parse (everything which is not a map or a struct). If you are in a debugging session you will print an error message instead. Sessions are opened by formatterInstance.StartDebug() and closed by formatterInstance.EndDebug()

[source, go]

formatter = JSONFormatter{} formatter.StartDebug() formatter.Print("Invalid String") //Outputs ""Invalid String" is a non supported data, please use map or struct" formatter.EndDebug()