First, the caveat. I know error handling is a long-standing discussion. I
know there has been lots of debate on error handling, and it can seem like
there are no more new ideas to be had on the topic. And I have looked at
several/most of the most popular proposals, and there are quite a few that
bear similarity but are critically different in important aspects to this
proposal. If this has been proposed before with the same effective
fingerprint, I haven't been able to find it after several hours of due
diligence. I'm interested in hearing any and all (well-reasoned) thoughts
on the matter, but if there's a flaw in my logic, I don't see it yet.
In short, the proposal is to create a conditional return statement, e.g. "
returnif" of the form:
returnif [bool], [returnvalue],...
This is syntactic sugar for:
if [bool] {
return [returnvalue],...
}
of which, the immediate benefit is:
returnif err!=nil, err
or alternatively:
returnif myErrorChecker(err), myErrorWrapper(err, "Some text.")
Here's my reasoning. Go Error Handling in is current form is extremely
correct, precise, explicit, and clear. All very good things. Really the
only problem with it is the repetitious verbosity. A programmer's
instinctive reaction to repetitious verbosity is to wrap it in a function.
The infamous "if err != nil {return err}", although repetitious and
ubiquitous, cannot effectively be encapsulated to "return someErrorChecker()",
because the return statement is unconditional. Once I start a statement
with return, nothing I can do later in the statement or within a called
function can change whether or how that return alters flow control. This,
I think, is the quintessential problem with the current error handling
methodology. This proposal addresses that without sacrificing any of the
good things about error handling in Go. Error handling is still explicit.
Errors can still be treated as values. Proper error handling and annotating
is blessed but optional. The behavior of defer is unaffected. It is still
simple to understand, and easy to read. And it's entirely backwards
compatible.
Also, while the most obvious benefit is in error handling, this is not
technically just an error handling solution. It is completely unopinionated
on the type of values it returns, or whether they qualify as an error or
not. I can foresee enterprising gophers finding other uses for this
keyword, and quite possibly even new useful design patterns could emerge as
a result.
Possible Objections:
- It could be seen to violate the "one way to do things" principle.
However,
1. It violates this rule much less than almost all of the other
proposals for error handling.
2. If, under the covers, it's just code substitution, then there's
still only one actual avenue of execution in the compiled objects.
3. There is precedent for this type of shortcut when the benefits are
so widespread and the sugar improves readability. For example,
} else if isTrue {
doSomething()
}
is sugar for
} else {
if isTrue {
doSomething()
}
}
- "It's just a variation on other existing proposals."
- This proposal avoids or addresses all the objections listed in the
error
handling meta issue #40432 <https://github.com/golang/go/issues/40432>,
and as such, may be a variation, but varies sufficiently to create a
different result set.
- From the meta issue:
- The check/handle proposal
<https://go.googlesource.com/proposal/+/master/design/go2draft-error-handling.md>
.
- One major reason this was rejected was a lack of clarity
between handle and defer.
- The try proposal <https://golang.org/issue/32437>.
- One major reason this was rejected was the additional flow
control: a complex expression using try could cause the function to
return.
Go currently has no flow control constructs at the expression
level, other
than panic which does more than just return from a function.
- Special characters, often ! or ?, that insert an error check
in a function call or assignment.
- These are typically rejected because they are cryptic. Often
a single ! or other character leads to a change in flow control.
- Simplifications of if err != nil, to reduce boilerplate.
- These are typically rejected either because they don't reduce
the boilerplate enough to make it worth changing the language, or
because
they are cryptic.
- What about edge cases? How to handle else clauses or additional
conditional logic based on error type etc.?
- It's my belief that else clauses too rare to justify additional
syntax. If you need an else/else if clause, you can use the existing
syntax and lay out your conditionals on more lines. Also - you know - any
code after a return statement is essential an else clause anyway.
- By making [bool] an expression, any additional logic may be handled
by the programmer in a determinant function that returns a boolean. This
puts this type of flow control in the hands of the developer.
- The short statement currently available with if and for statements (if
err:=doSomething(); err != nil) could be implemented in a similar
fashion, but my personal vote would be to disallow it, as most of the
simplicity and clarity of this proposal could be lost down that rabbit
hole.
I believe the most critical difference between this proposal and previous
ones is that this proposal addresses the core issue more directly. The
central problem to the current error handling methodology is not actually
specific to error handling. That's just where it's most visible. The core
problem is essentially the fact that a child function cannot affect the
conditional return of a parent function (barring further conditional
logic), even with explicit permission by the parent function. This is not
true with any other form of flow control. This is why the current
methodology feels wrong to developers, because they are disallowed from
encapsulating repetitious logic in a way that is consistent with other flow
control statements.
Anyway, that's my argument. If anyone knows of a previous proposal that
this duplicates, and/or knows why that one didn't/couldn't work, I'd be
grateful for the explanation.
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