err 1.0.0

Error data structures for fine-grained control over errors. It is possible to use errors as values like in Go

Err

Error data structures for fine-grained control over errors. It is possible to use errors as values like in Go

The Err class

import 'package:err/err.dart';

// Create an error:
final err = Err.error("An error has occured");

// Use with a function as return value 
Err theFunction() {
  try {
    // something wrong
  } catch (e) {
    return Err.error(e);
  }
  return null;
  // or to not use a null value return an empty error object
  return const Err.nil();
}

Check the error:

final err = theFunction();
if (err != null) {
   // print the error to the console
   err.console();
   // throw an exception from the error
   err.raise();
}
// or if not using null values
if (!err.isNil) {
   print("${err.date} ${err.type} : ${err.message}");
}

Data structure:

/// An error message for the user
final String userMessage;

/// The date of the error
DateTime get date;

/// The error type
ErrType get type;

/// Get an exception from the message
Exception get exception;

/// Get the message
String get message;

/// Is the error empty
bool get isNil;

Available error levels:

enum ErrType { critical, error, warning, info, debug }

Constructors

All the constructors accept either a String, an Exception or an Error as input

/// Critical error
final err = Err.critical("The error message");

/// Error
final err = Err.error("The error message");

/// Warning
final err = Err.warning("The warning message");

/// Info
final err =
   Err.info("The info message", userMessage: "A nice message for the user");

/// Debug
final err = Err.debug("The debug message");   

// from a type
final err = Err.fromType("The error message", ErrType.warning);

// duplicate an error adding a message for the user
final niceErr = err.copyWithUserMessage("A nice error message")
print("Message for the developer: ${niceErr.message}");
print("Message for the user: ${niceErr.userMessage}");

The userMessage parameter is optional for all constructors

Print an error

Print an error to console, similar to console.log in javascript:

/// print an instance
err.console();
/// print from a string or an [Err]
Err.log("An error");

Error as values

A data structure is available to pass return values of functions with errors: the ÈrrPack class:

import 'package:err/err.dart';

ErrPack<int> _someFunctionThatReturnsAnInt() {
  try {
    throw Exception("Oops");
  } catch (e) {
    // return an error and no value
    return ErrPack.err(Err.warning(e));
  }
  // return no error and a integer value
  return const ErrPack.ok(1);
}

ErrPack<Null> _someFunctionThatReturnsNull() {
  try {
    // ok
  } catch (e) {
    // return an error and no value
    return ErrPack.err(Err.debug("Something went wrong"));
  }
  // return no error and a null value
  return const ErrPack.nullOk();
}

void main() {
  _someFunctionThatReturnsNull().throwIfError();
  // or
  final res = _someFunctionThatReturnsAnInt();
  if (res.hasError) {
    // print the error
    res.log();
    // throw
    res.raise();
  }
  // get the return value
  final int i = res.value;
}