Raise Error In Ruby

users never enter incorrect data, and resources are plentiful and cheap. Well, that's about to change. Welcome to the real world! In the real world, errors happen. Good programs (and programmers) anticipate them and arrange to handle them gracefully. This isn't always as easy as

Ruby Raise Custom Exception

it might be. Often the code that detects an error does not have the context to ruby exception handling best practices know what to do about it. For example, attempting to open a file that doesn't exist is acceptable in some circumstances and is a ruby rescue syntax fatal error at other times. What's your file-handling module to do? The traditional approach is to use return codes. The open method returns some specific value to say it failed. This value is then propagated back through the layers of

Ruby Finally

calling routines until someone wants to take responsibility for it. The problem with this approach is that managing all these error codes can be a pain. If a function calls open, then read, and finally close, and each can return an error indication, how can the function distinguish these error codes in the value it returns to its caller? To a large extent, exceptions solve this problem. Exceptions let you package up information about an error into an object.

Ruby Throw Vs Raise

That exception object is then propagated back up the calling stack automatically until the runtime system finds code that explicitly declares that it knows how to handle that type of exception. The Exception Class The package that contains the information about an exception is an object of class Exception, or one of class Exception's children. Ruby predefines a tidy hierarchy of exceptions, shown in Figure 8.1. As we'll see later, this hierarchy makes handling exceptions considerably easier. Figure 8.1 not available... When you need to raise an exception, you can use one of the built-in Exception classes, or you can create one of your own. If you create your own, you might want to make it a subclass of StandardError or one of its children. If you don't, your exception won't be caught by default. Every Exception has associated with it a message string and a stack backtrace. If you define your own exceptions, you can add additional information. Handling Exceptions Our jukebox downloads songs from the Internet using a TCP socket. The basic code is simple: opFile = File.open(opName, "w") while data = socket.read(512) opFile.write(data) end What happens if we get a fatal error halfway through the download? We certainly don't want to store an incomplete song in the song list. “I Did It My *click*”. Let's add some exception handling code and see how it helps. We enclose the code that could raise an e

regexp.rdoc security.rdoc standard_library.rdoc syntax.rdoc assignment.rdoc calling_methods.rdoc control_expressions.rdoc exceptions.rdoc literals.rdoc methods.rdoc miscellaneous.rdoc modules_and_classes.rdoc precedence.rdoc refinements.rdoc README.ja.rdoc README.rdoc ruby raise argumenterror Class/Module Index Quicksearch ArgumentError Array BasicObject Bignum Binding

Ruby Begin

Class Comparable Complex Complex::compatible ConditionVariable Continuation Data Dir ENV EOFError Encoding Encoding::CompatibilityError ruby standard error Encoding::Converter Encoding::ConverterNotFoundError Encoding::InvalidByteSequenceError Encoding::UndefinedConversionError EncodingError Enumerable Enumerator Enumerator::Generator Enumerator::Lazy Enumerator::Yielder Errno Exception FalseClass Fiber FiberError File File::Constants File::Stat FileTest http://phrogz.net/programmingruby/tut_exceptions.html Fixnum Float FloatDomainError GC GC::Profiler Hash IO IO::EAGAINWaitReadable IO::EAGAINWaitWritable IO::EINPROGRESSWaitReadable IO::EINPROGRESSWaitWritable IO::EWOULDBLOCKWaitReadable IO::EWOULDBLOCKWaitWritable IO::WaitReadable IO::WaitWritable IOError IndexError Integer Interrupt Kernel KeyError LoadError LocalJumpError Marshal MatchData Math Math::DomainError Method Module Mutex NameError NilClass NoMemoryError NoMethodError NotImplementedError Numeric Object ObjectSpace ObjectSpace::WeakMap Proc https://ruby-doc.org/core-2.2.0/RuntimeError.html Process Process::GID Process::Status Process::Sys Process::UID Process::Waiter Queue Random Range RangeError Rational Rational::compatible Regexp RegexpError RubyVM RubyVM::Env RubyVM::InstructionSequence RuntimeError ScriptError SecurityError Signal SignalException SizedQueue StandardError StopIteration String Struct Symbol SyntaxError SystemCallError SystemExit SystemStackError Thread Thread::Backtrace::Location ThreadError ThreadGroup Time TracePoint TrueClass TypeError UnboundMethod UncaughtThrowError ZeroDivisionError fatal unknown No matching classes. RuntimeError A generic error class raised when an invalid operation is attempted. [1, 2, 3].freeze << 4 raises the exception: RuntimeError: can't modify frozen Array Kernel#raise will raise a RuntimeError if no Exception class is specified. raise "ouch" raises the exception: RuntimeError: ouch Commenting is here to help enhance the documentation. For example, code samples, or clarification of the documentation. If you have questions about Ruby or the documentation, ple

here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us Learn more about Stack Overflow the company Business Learn more about hiring developers http://stackoverflow.com/questions/4800698/what-is-the-difference-between-raise-foo-and-raise-exception-newfoo or posting ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x http://www.skorks.com/2009/09/ruby-exceptions-and-exception-handling/ Dismiss Join the Stack Overflow Community Stack Overflow is a community of 6.2 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up What is the difference between `raise “foo”` and `raise Exception.new(“foo”)`? up vote 61 down vote favorite 18 What is the difference - technical, philosophical, conceptual, or otherwise - between raise "foo" and raise Exception.new("foo") ruby raise ? ruby exception exception-handling share|improve this question asked Jan 26 '11 at 1:40 John Bachir 8,261881153 add a comment| 2 Answers 2 active oldest votes up vote 69 down vote accepted Technically, the first raises a RuntimeError with the message set to "foo", and the second raises an Exception with the message set to "foo". Practically, there is a significant difference between when you would want to use the former and when you want to use the latter. Simply put, raise error in you probably want a RuntimeError not an Exception. A rescue block without an argument will catch RuntimeErrors, but will NOT catch Exceptions. So if you raise an Exception in your code, this code will not catch it: begin rescue end In order to catch the Exception you will have to do this: begin rescue Exception end This means that in a sense, an Exception is a "worse" error than a RuntimeError, because you have to do more work to recover from it. So which you want depends on how your project does its error handling. For instance, in our daemons, the main loop has a blank rescue which will catch RuntimeErrors, report them, and then continue. But in one or two circumstances, we want the daemon to really really die on an error, and in that case we raise an Exception, which goes straight through our "normal error handling code" and out. And again, if you are writing library code, you probably want a RuntimeError, not an Exception, as users of your library will be surprised if it raises errors that a blank rescue block can't catch, and it will take them a moment to realize why. Finally, I should say that the RuntimeError is a subclass of the StandardError class, and the actual rule is that although you can raise any type of object, the blank rescue will by default only catch anything that inherits from StandardError.

deals with exceptions is strikingly similar to other languages (such as Java etc.). But, I think all the stuff I've been writing about Ruby lately has taken on a life of it's own for me :), so I am going to quickly go over this topic if only for completeness sakes. Raising Exceptions Getting Ruby to raise an exception is easy :). Ruby, like many other languages has a hierarchy of exception classes (that all inherit from the class Exception), some of these are familiar and fairly easy to produce, for example ZeroDivisionError or NoMethodError. Here is some code which will do just that: 1/0 or blah = Object.new blah.hello Of course you don't have to wait for Ruby to raise exceptions for you, you can do so explicitly in your code with the raise keyword (it is actually a method). Lets write a method where we explicitly raise an exception if the argument we pass in is false: def i_must_have_truth(value) raise TypeError, 'You must give me truth' if value == false end i_must_have_truth false this prints: D:\ruby-projects\scrap\lib\scrap.rb:15:in `i_must_have_truth': You must give me truth (TypeError) from D:\ruby-projects\scrap\lib\scrap.rb:18 As you can see we are able to raise a specific exception and pass it a message which then gets printed out to the console. There is also a handy shortcut, if you use raise without giving it a specific exceptions (or even without giving it an error message to display), Ruby will automatically raise a RuntimeException for you which is pretty handy: def i_must_have_truth(value) raise "Hello" end i_must_have_truth false this prints: D:\ruby-projects\scrap\lib\scrap.rb:15:in `i_must_have_truth': Hello (RuntimeError) from D:\ruby-projects\scrap\lib\scrap.rb:18 Rescuing Exceptions So far so good, but life would be pretty tough if we couldn't handle the exceptions that get thrown in any way, This is where the rescue clause comes in. If