4 ms·

I'd arguee Go's string type is "somewhat unusable"* since it doesn't enforce the guarantees it says/implies it does. The byte slice it points to is not guarante

I'd arguee Go's string type is "somewhat unusable"* since it doesn't enforce the guarantees it says/implies it does. The byte slice it points to is not guaranteed to be valid utf8. * of course to a degree, let's be reasonable, it's usable in a _lot_ of contexts, but I like my types to actually mean something.

37ef_ced3 6y ago
In Go, malformed UTF-8 encodings are expected They are handled in a well-defined and graceful manner by all aspects of the language, runtime, and library
DougBTX 6y ago
Go doesn't guarantee any encoding for strings, very deliberately (so that, eg, they can be used to represent file names).
- KMag 6y ago
  Filesystem paths are not strings. Linux doesn't enforce an encoding. Windows at least didn't used to enforce proper use of conjugate UTF-16 pairs (see WTF-8 encoding). I think OS X does perform UTF-8 normalization, which might include sanity checking and rejecting malformed UTF-8, but I'm not sure. A byte array (or a ref-counted singly-linked list of immutable byte arrays to save space/copying) is a much better representation for a file system path. That doesn't have great interaction with GUIs, but there are other corner cases that are often problematic for GUIs. In high school, one of my friends had a habit of putting games on the school library computers, and renaming them to names with non-printable characters using alt+number pad. (He used 129, IIRC, which isn't assigned a character in CP-1252.) The Windows 95 graphical shell would convert the non-printable characters to spaces for display, but when the librarian tried to delete the games, it would pass the display name to the kernel, which would complain that the presented path didn't exist.
  - jerf 6y ago
    It is not clear to me if you're elaborating or think you're disagreeing, but that is what Go does. It is generally assumed in Go that strings are UTF-8, but in practice what they actually are are just bags of bytes. Nothing really "UTF-y" will happen to them until you directly call UTF functions on them, which may produce new strings. It's something that I don't think could work unless your language is as recent as Go, and perhaps even Go 1.0 was pushing it, but it is an increasingly viable answer. For as thin as Go's encoding support really is in some sense, it has almost never caused me any trouble. The contexts where you are actively unsafe in assuming UTF-8 are decreasing, and the ones that are going to survive are the ones where there's some sort of explicit label, like in email. (Not that those are always trustworthy either.)
    - KMag 6y ago
      I'm saying it's useful to have valid strings and paths as separate types, but Go conflates the two types. Conflating the two is likely to lead to confused usage (such as programmers assuming there's a bijective mapping between valid paths and valid sequences of Unicode codepoints.) Pervasive confused usage of this sort in the wild in Python 2 was the motivation behind splitting bytes and strings in Python 3.
      - jerf 6y ago
        As you pointed out, path types are awfully specialized to the OS and really even the file system itself. It is not clear that "Go" could provide such a thing. It doesn't need to, really, you can relatively easily create a type for the specific case you have. type PathSegment struct { path string // not exported, so only the empty one can be created externally } func MakePath(in string) (PathSegment, error) { // validate the input here } You'll need some more supporting types, of course, but it doesn't have to be provided by "Go" itself. (I have something rather like this in my codebase, though it is specialized to just Unix paths since I have no need to care about all the cross-platform details in this code base.) I wouldn't expect this to be something the language itself provides, and I'm not even that worried about it being missing from the standard library because it's awfully detail-oriented even for that.
throwaway894345 6y ago
I think of a string as an immutable byte slice. This is a little confusing since the language supports utf-8 literals only and it also lets you iterate over individual runes with for loops, but those are just conveniences over the fact that these are really just immutable byte slices. You could probably make your own “UTF8” type with the invariants you want (or at least someone would have to drop down into unsafe to violate the invariants) but in general Go programs don’t typically go that far, presumably because it doesn’t add much value in practice, which would suggest that your “somewhat unusable” claim (even with its caveat) is too strong. That said, I think it would be nice if Go made it a little easier/clearer to model a type that can only be created by a particular constructor or some such.
skybrian 6y ago
Go's standard library works with both possibly-malformed and verified UTF-8 strings, which is a nice property. The type system needed to explain what they actually do (take one of two possible input types and return the corresponding output type) would require generics, which we don't have yet. An alternative would be to duplicate the code to account for the different types, but we already have that for []byte versus string and that's bad enough already.

37ef_ced3 6y ago

In Go, malformed UTF-8 encodings are expected They are handled in a well-defined and graceful manner by all aspects of the language, runtime, and library

DougBTX 6y ago

Go doesn't guarantee any encoding for strings, very deliberately (so that, eg, they can be used to represent file names).

KMag 6y ago
Filesystem paths are not strings. Linux doesn't enforce an encoding. Windows at least didn't used to enforce proper use of conjugate UTF-16 pairs (see WTF-8 encoding). I think OS X does perform UTF-8 normalization, which might include sanity checking and rejecting malformed UTF-8, but I'm not sure. A byte array (or a ref-counted singly-linked list of immutable byte arrays to save space/copying) is a much better representation for a file system path. That doesn't have great interaction with GUIs, but there are other corner cases that are often problematic for GUIs. In high school, one of my friends had a habit of putting games on the school library computers, and renaming them to names with non-printable characters using alt+number pad. (He used 129, IIRC, which isn't assigned a character in CP-1252.) The Windows 95 graphical shell would convert the non-printable characters to spaces for display, but when the librarian tried to delete the games, it would pass the display name to the kernel, which would complain that the presented path didn't exist.
- jerf 6y ago
  It is not clear to me if you're elaborating or think you're disagreeing, but that is what Go does. It is generally assumed in Go that strings are UTF-8, but in practice what they actually are are just bags of bytes. Nothing really "UTF-y" will happen to them until you directly call UTF functions on them, which may produce new strings. It's something that I don't think could work unless your language is as recent as Go, and perhaps even Go 1.0 was pushing it, but it is an increasingly viable answer. For as thin as Go's encoding support really is in some sense, it has almost never caused me any trouble. The contexts where you are actively unsafe in assuming UTF-8 are decreasing, and the ones that are going to survive are the ones where there's some sort of explicit label, like in email. (Not that those are always trustworthy either.)
  - KMag 6y ago
    I'm saying it's useful to have valid strings and paths as separate types, but Go conflates the two types. Conflating the two is likely to lead to confused usage (such as programmers assuming there's a bijective mapping between valid paths and valid sequences of Unicode codepoints.) Pervasive confused usage of this sort in the wild in Python 2 was the motivation behind splitting bytes and strings in Python 3.
    - jerf 6y ago
      As you pointed out, path types are awfully specialized to the OS and really even the file system itself. It is not clear that "Go" could provide such a thing. It doesn't need to, really, you can relatively easily create a type for the specific case you have. type PathSegment struct { path string // not exported, so only the empty one can be created externally } func MakePath(in string) (PathSegment, error) { // validate the input here } You'll need some more supporting types, of course, but it doesn't have to be provided by "Go" itself. (I have something rather like this in my codebase, though it is specialized to just Unix paths since I have no need to care about all the cross-platform details in this code base.) I wouldn't expect this to be something the language itself provides, and I'm not even that worried about it being missing from the standard library because it's awfully detail-oriented even for that.

throwaway894345 6y ago

I think of a string as an immutable byte slice. This is a little confusing since the language supports utf-8 literals only and it also lets you iterate over individual runes with for loops, but those are just conveniences over the fact that these are really just immutable byte slices. You could probably make your own “UTF8” type with the invariants you want (or at least someone would have to drop down into unsafe to violate the invariants) but in general Go programs don’t typically go that far, presumably because it doesn’t add much value in practice, which would suggest that your “somewhat unusable” claim (even with its caveat) is too strong. That said, I think it would be nice if Go made it a little easier/clearer to model a type that can only be created by a particular constructor or some such.

skybrian 6y ago

Go's standard library works with both possibly-malformed and verified UTF-8 strings, which is a nice property. The type system needed to explain what they actually do (take one of two possible input types and return the corresponding output type) would require generics, which we don't have yet. An alternative would be to duplicate the code to account for the different types, but we already have that for []byte versus string and that's bad enough already.