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CooperCorona/CoronaErrors
Commonly used patterns for error handling in Swift
.package(url: "https://github.com/CooperCorona/CoronaErrors.git", from: "2.0.4")

CoronaErrors

Collection of convenience types, methods, and an exception hierarchy to make error handling easier.

See https://coopercorona.github.io/CoronaErrors/ for API documentation.

Errors

All Error types are enums conforming to the Error protocol. Each type logically groups together similar types of errors. All Error types have a corresponding Exception type.

IOError

Occurs when an input/output operation cannot be completed.

  • fileNotFound: A file or directory does not exist at a given path.
  • permissionDenied: The program does not have permission to access the file or directory at a given path.

OperationError

Occurs when an operation cannot be completed.

  • alreadyExists: The target of an operation already exists.
  • missing: The target of an operation does not exist.

ParseError

Occurs when parsing some object into a different kind of object.

  • incorrectFormat: The format of the original object is incorrect and cannot be converted to the new object.
  • notEnoughComponents: The format of the original object requires a specific number of logical components to convert, but not enough components were provided.
  • tooManyComponents: The format of the original object requires a specific number of logical components to convert, too many components were provided.

ValueError

Occurs when the value of a variable is incorrect in some way.

  • invalidArgument: An argument to a function has an incorrect value.
  • nil: A value is nil when a value should exist.
  • invalidState: A variable has an incorrect value. Similar to invalidArgument except it doesn't assume the variable in question is a function's argument.

Exceptions

Exceptions encapsulate an Error and additional metadata, including a explanatory message and stack trace. Exception conforms to Error, so it can be thrown and caught like any other Error. Subclasses are used to provide additional contextual information and allow more specific catch statements.

Exceptions can be caught as follows:

func throwException() { throw Exception(error: ValueError.nil, message: "nil")
do {
  try throwException()
} catch let error as Exception {
  // Do something with the error...
}

Specific underlying errors can be caught using a where clause:

func throwException() { throw Exception(error: ValueError.nil, message: "nil")
do {
  try throwException()
} catch let error as Exception where error.error == ValueError.nil {
  // Do something with the error...
}

Subclasses of Exception can override descriptionComponents to include additional information in the string representation of the Exception. Subclasses must call the super implementation and prepend it to their custom components.

IOException

An exception caused by an IOError.

FileNotFoundException

An IOException caused by an IOError.fileNotFound error.

NilException

An exception caused by a ValueError.nil error. Parameterized based on the type of variable that is nil. To catch any type of NilException irrespective of type, catch AnyNilException. This is required because NilException<T> cannot be cast to NilException<U>, regardless of whether T can be cast to U, so trying to catch NilException<Any> will fail.

OperationError

An exception caused by an OperationError.

ParseException

An exception caused by a ParseError.

ValueError

An exception caused by a ValueError. Exposes the value whose incorrectness caused the exception. ValueError<T>.expected constructs a ValueError instance by passing in an expected value along with an actual value, automatically setting the message property to explain what value was expected.

GitHub

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Last commit: 5 weeks ago

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iOS Software Engineer @ Perry Street Software
Perry Street Software is Jack’d and SCRUFF. We are two of the world’s largest gay, bi, trans and queer social dating apps on iOS and Android. Our brands reach more than 20 million members worldwide so members can connect, meet and express themselves on a platform that prioritizes privacy and security. We invest heavily into SwiftUI and using Swift Packages to modularize the codebase.

Swiftpack is being maintained by Petr Pavlik | @ptrpavlik | @swiftpackco | API