Is function parameter validation using errors a good pattern in Go?

Question

Is parameter validation using error return codes considered good practice ? I mean where should somebody use errors vs panics (are there any guidelines?).

For instance:

• Is checking for non-nil + returning an error if it is nil a good practice ?
• Or checking for correct integer ranges etc.

I imagine that using errors that often would make Go feel very C-ish and would look pretty bad. Are panics a good alternative in those situations ?

Or should a Gopher use the Python/Ruby/JS-approach "just let it fail" ?

I'm a bit confused because panics are for real "errors" in my understanding. But using errors all the time is just bad.

And even if I would return error code: What could I do if somebody passes wrong parameter to my function but ignores the errors codes ? -> Nothing! So honestly I would say panics are nice for those situations but in a language where error codes are used over panics this is not very clear.

Answer 1

"Escaping" panics¹ in Go (I mean, those which might be produced by the functions comprising the public API of your package) are to deal with errors programmers do. So, if your function gets a pointer to an object, and that can't be nil (say, to indicate that the value is missing) just go on and dereference the pointer to make the runtime panic itself if it happens to be nil. If a function expects an integer that must be in a certain range, panic if it's not in that range — because in a correct program all values which might be passed to your function are in that range, and if they don't then either the programmer failed to obey the API or they did not sanitize the value acquired from the outside which, again, is not your fault.

On the other hand, problems like failure to open a file or pefrorm some other action your function is supposed to perform when called correctly should not cause panics and the function should return an appropriate error instead.

Note that the recommendation for explicit checking for null parameters in the functions of public APIs in .NET and Java code has different goal of making such kinds of errors sort-of more readable. But since 99% of .NET and Java code just lets all the exceptions propagate to the top level (and then be displayed or may be logged) it's just replacing one (generated by runtime) exception with another. It might make errors more obvious—the execution fails in the API function, not somewhere deeper down the call stack—but adds unnecessary cruft to these API functions. So yes, this is opinionated but my subjective opinion is: to let it just crash is OK in Go—you'll get a descriptive stack trace.

TL;DR

With regard to processing of run-time problems,

• panics are for programming errors;
• returning errors is for problems with carrying out the intended tasks of functions.

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¹ Another legitimate use for panics is quick "cold-path" returning from deep recursive processing/computation; in this case panic should be caught and processed by your package, and the corresponding public API functions should return errors. See this and this for more info.