# README
= 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()