4 ms·

> Go really wants you to define a type that you can cast or switch on, which is far better. Go very very much does not want application code to be type-asserti

by kiitos 1y ago

> Go really wants you to define a type that you can cast or switch on, which is far better. Go very very much does not want application code to be type-asserting the values they receive. `switch x.(type)` is an escape hatch, not a normal pattern! And for errors especially so! > they tend to use errors.New and fmt.Errorf which do not lend themselves to branching on error conditions You almost never need to branch on error conditions in the sense you mean here. 90% of the time, err != nil is enough. 9% of the time, errors.Is is all you need, which is totally satisfied by fmt.Errorf.

stouset 1y ago
> 90% of the time, err != nil is enough Only if your only desire is to bubble the error up and quite literally not handle it at all. If you want to actually handle an error, knowing what actually went wrong is critical.
- kiitos 1y ago
  Returning an error -- or, more accurately, identifying an error and returning an annotation or transformation of that error appropriate for your caller -- is a way of handling it. The cases where, when your code encounters an error, that it can do anything other than this are uncommon.
  - stouset 1y ago
    This goes completely against the golang error-handling mindset. Error handling is so important, we must dedicate two-thirds of the lines of every golang program to it. It is so important that it must be made a verbose, manual process. But there's also nothing that can be done about most errors, so we do all this extra work only to bubble errors up to the top of the program. And we do all this work as a human exception-handle to build up a carefully curated manual stack trace that loses all the actually-useful elements of a stack trace like filenames and line numbers.
  - tinthedev 1y ago
    This is just nonsense. Handling errors this way is possible in only very brittle and simplistic software. I mean, you're contradicting your very own argument. If this was the primary/idiomatic way of handling errors... then Go should just go the way of most languages with Try/Catch blocks. If there's no valuable information or control flow to managing errors... then what's the point of forcing that paradigm to be so verbose and explicit in control flow? None.
packetlost 1y ago
> Go very very much does not want application code to be type-asserting the values they receive. `switch x.(type)` is an escape hatch, not a normal pattern! And for errors especially so! A type assert/switch is exactly how you implement Error.Is [^0] if you define custom error types. Sure it's preferable to use the interface method in case the error is wrapped, but the point stands. If you define errors with Errors.New you use string comparison, which is only convenient if you export a top level var of the error instead of using Errors.New directly. > You almost never need to branch on error conditions in the sense you mean here. 90% of the time, err != nil is enough. 9% of the time, errors.Is is all you need, which is totally satisfied by fmt.Errorf. I'd argue it's higher than 9% if you're dealing with IO, which most applications will. Complex interfaces like HTTP and filesystems will want to retry on certain conditions such as timeouts, for example. Sure most error checks by volume might be satisfied with a simple nil check, it's not fair to say branching on specific errors is not common. [0]: The documentations own example of implementing Error.Is uses a switch. https://cs.opensource.google/go/go/+/refs/tags/go1.24.3:src/syscall/syscall_unix.go;l=120 https://cs.opensource.google/go/go/+/refs/tags/go1.24.3:src/... It happens to be a syscall interface so errors are reported as numbers.
- Yoric 1y ago
  > If you define errors with Errors.New you use string comparison. With `Errors.New`, you're expected to provide a human-readable message. By definition, this message may change. Relying on this string comparison is a recipe for later breakages. But even if it worked, this would require documenting the exact error string returned by the function. Have you _ever_ seen a function containing such information in the documentation? As for `switch x.(type)`, it doesn't support any kind of unwrapping, which means that it's going to fail if someone in the stack just decides to add a `fmt.Errorf` along the way. So you need all the functions in the stack to promise that they're never going to add an annotation detailing what the code was doing when the error was raised. Which is a shame, because `fmt.Errorf` is often a good practice.
  - packetlost 1y ago
    I was actually referring to the implementation of errors.Is, which uses string comparison internally if you use the error type returned by errors.New and a type cast or switch if you use a custom type (or the cases where the stdlib defines a custom error type).

by kiitos 1y ago

stouset 1y ago

> 90% of the time, err != nil is enough Only if your only desire is to bubble the error up and quite literally not handle it at all. If you want to actually handle an error, knowing what actually went wrong is critical.

kiitos 1y ago
Returning an error -- or, more accurately, identifying an error and returning an annotation or transformation of that error appropriate for your caller -- is a way of handling it. The cases where, when your code encounters an error, that it can do anything other than this are uncommon.
- stouset 1y ago
  This goes completely against the golang error-handling mindset. Error handling is so important, we must dedicate two-thirds of the lines of every golang program to it. It is so important that it must be made a verbose, manual process. But there's also nothing that can be done about most errors, so we do all this extra work only to bubble errors up to the top of the program. And we do all this work as a human exception-handle to build up a carefully curated manual stack trace that loses all the actually-useful elements of a stack trace like filenames and line numbers.
- tinthedev 1y ago
  This is just nonsense. Handling errors this way is possible in only very brittle and simplistic software. I mean, you're contradicting your very own argument. If this was the primary/idiomatic way of handling errors... then Go should just go the way of most languages with Try/Catch blocks. If there's no valuable information or control flow to managing errors... then what's the point of forcing that paradigm to be so verbose and explicit in control flow? None.

packetlost 1y ago

> Go very very much does not want application code to be type-asserting the values they receive. `switch x.(type)` is an escape hatch, not a normal pattern! And for errors especially so! A type assert/switch is exactly how you implement Error.Is [^0] if you define custom error types. Sure it's preferable to use the interface method in case the error is wrapped, but the point stands. If you define errors with Errors.New you use string comparison, which is only convenient if you export a top level var of the error instead of using Errors.New directly. > You almost never need to branch on error conditions in the sense you mean here. 90% of the time, err != nil is enough. 9% of the time, errors.Is is all you need, which is totally satisfied by fmt.Errorf. I'd argue it's higher than 9% if you're dealing with IO, which most applications will. Complex interfaces like HTTP and filesystems will want to retry on certain conditions such as timeouts, for example. Sure most error checks by volume might be satisfied with a simple nil check, it's not fair to say branching on specific errors is not common. [0]: The documentations own example of implementing Error.Is uses a switch. https://cs.opensource.google/go/go/+/refs/tags/go1.24.3:src/syscall/syscall_unix.go;l=120 https://cs.opensource.google/go/go/+/refs/tags/go1.24.3:src/... It happens to be a syscall interface so errors are reported as numbers.

Yoric 1y ago
> If you define errors with Errors.New you use string comparison. With `Errors.New`, you're expected to provide a human-readable message. By definition, this message may change. Relying on this string comparison is a recipe for later breakages. But even if it worked, this would require documenting the exact error string returned by the function. Have you _ever_ seen a function containing such information in the documentation? As for `switch x.(type)`, it doesn't support any kind of unwrapping, which means that it's going to fail if someone in the stack just decides to add a `fmt.Errorf` along the way. So you need all the functions in the stack to promise that they're never going to add an annotation detailing what the code was doing when the error was raised. Which is a shame, because `fmt.Errorf` is often a good practice.
- packetlost 1y ago
  I was actually referring to the implementation of errors.Is, which uses string comparison internally if you use the error type returned by errors.New and a type cast or switch if you use a custom type (or the cases where the stdlib defines a custom error type).