Implement Error Handling
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What Is Error Handling
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voted up and rise to the top How to Implement Error Handling [closed] up vote 8 down vote favorite 7 Even though I've programmed on a professional level for some years I still do not fully understand error handling. Although my applications work fine, the error handling isn't implemented at a professional level and is a mix and match of a number of techniques. There is no structure behind my error handling. I'd like to learn and understand how it's implemented at a professional level. This is one area where I lack knowledge. When should I use an exceptions and when should I return a success status, to be checked in the logic flow? Is it OK to mix exception and returning a status? I code in C# mainly. c# .net coding-standards error-handling share|improve this question edited Sep 1 '14 at 14:15 gnat 21.7k1365129 asked Sep 9 '13 at 12:42 James Jeffery 320215 closed as too broad by gnat, svick, MichaelT, Eric King, Corbin March Sep 10 '13 at 12:46 There are either too many possible answers, or good answers would be too long for this format. Please add details to narrow the answer set or to isolate an issue that can be answered in a few paragraphs.If this question can be reworded to fit the rules in the help center, please edit the question. 1 Why down vote? I am asking a serious question about error handling implementation and how it's done. If this isn't the best place to ask such a question among programmers then where is? It really bugs me when people down vote such questions because there is no
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 or posting ads with us Programmers Questions Tags Users Badges Unanswered Ask Question _ Programmers Stack Exchange is a question and answer site for professional programmers interested in conceptual questions about software development. Join them; it only takes a minute: Sign up Here's how it works: Anybody can ask a http://programmers.stackexchange.com/questions/210900/how-to-implement-error-handling question Anybody can answer The best answers are voted up and rise to the top The modern way to perform error handling… up vote 104 down vote favorite 30 I've been pondering this problem for a while now and find myself continually finding caveats and contradictions, so I'm hoping someone can produce a conclusion to the following: Favour exceptions over error codes As far http://programmers.stackexchange.com/questions/147059/the-modern-way-to-perform-error-handling as I'm aware, from working in the industry for four years, reading books and blogs, etc. the current best practice for handling errors is to throw exceptions, rather than returning error codes (not necessarily an error code, but a type representing an error). But - to me this seems to contradict... Coding to interfaces, not implementations We code to interfaces or abstractions to reduce coupling. We don't know, or want to know, the specific type and implementation of an interface. So how can we possibly know what exceptions we should be looking to catch? The implementation could throw 10 different exceptions, or it could throw none. When we catch an exception surely we're making assumptions about the implementation? Unless - the interface has... Exception specifications Some languages allow developers to state that certain methods throw certain exceptions (Java for example, uses the throws keyword.) From the calling code's point of view this seems fine - we know explicitly which exceptions we might need to catch. But - this seems to suggest a... Leaky abstraction Why should an interface specify which exceptions can be thrown? What if the implementation doesn't need to
Mailing List Go on Google+ Go+ Community Go on Twitter Blog index The Go Blog Error handling and Go 12 July 2011 Introduction If you have written any Go code you have probably encountered the built-in error type. Go code uses error https://blog.golang.org/error-handling-and-go values to indicate an abnormal state. For example, the os.Open function returns a non-nil error value http://lisperator.net/pltut/real-samples/error-handling when it fails to open a file. func Open(name string) (file *File, err error) The following code uses os.Open to open a file. If an error occurs it calls log.Fatal to print the error message and stop. f, err := os.Open("filename.ext") if err != nil { log.Fatal(err) } // do something with the open *File f You can get a lot done in Go error handling knowing just this about the error type, but in this article we'll take a closer look at error and discuss some good practices for error handling in Go. The error type The error type is an interface type. An error variable represents any value that can describe itself as a string. Here is the interface's declaration: type error interface { Error() string } The error type, as with all built in types, is predeclared in the universe block. The most commonly-used implement error handling error implementation is the errors package's unexported errorString type. // errorString is a trivial implementation of error. type errorString struct { s string } func (e *errorString) Error() string { return e.s } You can construct one of these values with the errors.New function. It takes a string that it converts to an errors.errorString and returns as an error value. // New returns an error that formats as the given text. func New(text string) error { return &errorString{text} } Here's how you might use errors.New: func Sqrt(f float64) (float64, error) { if f < 0 { return 0, errors.New("math: square root of negative number") } // implementation } A caller passing a negative argument to Sqrt receives a non-nil error value (whose concrete representation is an errors.errorString value). The caller can access the error string ("math: square root of...") by calling the `error`'s Error method, or by just printing it: f, err := Sqrt(-1) if err != nil { fmt.Println(err) } The fmt package formats an error value by calling its Error() string method. It is the error implementation's responsibility to summarize the context. The error returned by os.Open formats as "open /etc/passwd: permission denied," not just "permission denied." The error returned by our Sqrt is missing information about the invalid argument. To add that information, a useful function is the fmt package's Errorf. It formats a string according to `Printf`'s rules and returns it as an error created by erro
constructs How fast are we? CPS Evaluator Guarding the stack Continuations Yield (advanced) Compiling to JS JS code generator CPS transformer Samples Improvements Optimizer Wrapping up Real samples Primitives catDir copyTree sequential copyTree parallel In fairness to Node Error handling Blog PL Tutorial UglifyJS SLip Sytes Home ➤ PL Tutorial ➤ Real samples ➤ Exceptions Error handling In the code on the previous page I discarded the if (err) throw new Error(err) lines. “Handling” errors in such a way is meaningless, because it forbids error recovery. We just throw, and the program aborts (unless you setup a global catch-all handler, but being global, it won't have enough context to nicely recover from the error). However, if you did anything serious in NodeJS you know that those lines are really necessary, in every callback. Except that, instead of throwing, it's a better idea to just pass the error to the previous callback (or handle it and recover if appropriate). The convention in NodeJS is that a callback will take an error as first argument, and the result as second. So we have to insert this line in every callback, right at the beginning: if (err) return callback(err). That's crude, to say the least. Exceptions in λanguage Thanks to explicit continuations, in λanguage we can implement an exception system that will work across asynchronous calls. We will implement a rudimentary system here—two primitives, TRY and THROW (uppercase, to avoid clashing with JavaScript's own try and throw keywords). Here's possible usage: TRY( λ() { let (data = readFile("/tmp/notexists")) { print("File contents:"); print(data); } } ## "ENOENT" means file not found , "ENOENT", λ(info){ print("File not found:", info); } ## generic handler , true, λ(info, code){ print("Some error. Code:", code, "info:", info); } ); It looks ugly because we don't extend the parser with new syntax—TRY and THROW are just plain functions. But if we wanted anything fancier, we could, of course, modify the parser. If you'd like to test this example, download the exception-enabled primitives. TRY receives a function and a bunch of error handlers. Each error handler must be preceded by the error code (so the number of arguments should be always odd). If true is passed instead of an error code, then that handler will be called for any error if not handled before. For the above to work, the primitive has been modified to call THROW (instead