error

The error composite of go-composites. An Error is the value carried by a Result: it follows the Null-Object grammar, so an "absence of error" is itself a real object (NullError) rather than a bare Go nil. Result.HasError() is simply !Error.IsNull(), which is why a fresh Result — whose error is a NullError — reports no error.

Install

go get github.com/go-composites/error

API

Error.Interface embeds the reflective Object.Interface (Kind, RespondTo, Methods) and adds:

method	returns	notes
Message()	string	the error text
IsNull()	bool	true only for NullError; false for a real error
Kind()	string	the interface kind, e.g. Error.Interface (from Object)
RespondTo(name)	bool	whether the value exposes a method named name
Methods()	[]string	the value's method names, via reflection

New(message string) Interface builds a concrete error with the given message (its IsNull() is false).

Subpackages

• error/src/object (Object) — the reflective base shared by every error type. Provides Kind, RespondTo and Methods, both as package functions over any interface{} and as the methods of the embedded Object.Interface.
• error/src/null (NullError) — the Null-Object error. New() yields an error whose Message() is "" and whose IsNull() is true; it is the default error of a fresh Result.
• error/src/method_not_implemented (MethodNotImplementedError) — a sentinel error. New(name string) formats "The method <name> is not implemented"; its IsNull() is false.

Usage

package main

import (
	"fmt"

	Error "github.com/go-composites/error/src"
	NullError "github.com/go-composites/error/src/null"
	NotImplemented "github.com/go-composites/error/src/method_not_implemented"
)

func main() {
	e := Error.New("key not found")
	fmt.Println(e.Message())  // key not found
	fmt.Println(e.IsNull())   // false

	none := NullError.New()
	fmt.Println(none.IsNull()) // true  -> a Result holding this HasError() == false

	nim := NotImplemented.New("Frobnicate")
	fmt.Println(nim.Message()) // The method Frobnicate is not implemented
}

License

BSD-3-Clause © the go-composites/error authors.