`bytevector-length' doesn't accept a shared array from a bytevector

`bytevector-length' doesn't accept a shared array from a bytevector

[Diogo F. S. Ramos]

I want to take the length of a shared array, but `bytevector-length'
throws an error claiming the shared array isn't a bytevector, even
though it prints the error argument as one.

--8<---------------cut here---------------start------------->8---
scheme@(guile-user)> ,use (rnrs bytevectors)
scheme@(guile-user)> (bytevector-length 
                      (make-shared-array (make-bytevector 42)
                                         list
                                         7))
ERROR: In procedure bytevector-length:
ERROR: In procedure scm_c_bytevector_length: Wrong type argument in position 1 (expecting bytevector): #vu8(0 0 0 0 0 0 0)

Entering a new prompt.  Type `,bt' for a backtrace or `,q' to continue.
scheme@(guile-user) [1]>
--8<---------------cut here---------------end--------------->8---

I am using Guile 2.0.11, Debian Stable package 2.0.11+1-9.

Re: `bytevector-length' doesn't accept a shared array from a bytevector

[Daniel Llorens]

On 21 Feb 2017, at 14:21, Diogo F. S. Ramos <dfsr@riseup.net> wrote:

> I want to take the length of a shared array, but `bytevector-length'
> throws an error claiming the shared array isn't a bytevector, even
> though it prints the error argument as one.
> 
> --8<---------------cut here---------------start------------->8---
> scheme@(guile-user)> ,use (rnrs bytevectors)
> scheme@(guile-user)> (bytevector-length 
>                      (make-shared-array (make-bytevector 42)
>                                         list
>                                         7))
> ERROR: In procedure bytevector-length:
> ERROR: In procedure scm_c_bytevector_length: Wrong type argument in position 1 (expecting bytevector): #vu8(0 0 0 0 0 0 0)
> 
> Entering a new prompt.  Type `,bt' for a backtrace or `,q' to continue.
> scheme@(guile-user) [1]>
> --8<---------------cut here---------------end--------------->8---
> 
> I am using Guile 2.0.11, Debian Stable package 2.0.11+1-9.
> 

This is addressed in 2.1, by eb3d623da57e6d31a58d95f932345fb761f9b701. Your example will print #1vu8(0 0 ...) to signify that it's not a bytevector. You can use array-length here.

I suppose the patch could be applied to 2.0.

Re: `bytevector-length' doesn't accept a shared array from a bytevector

[Diogo F. S. Ramos]

> On 21 Feb 2017, at 14:21, Diogo F. S. Ramos <dfsr@riseup.net> wrote:
>
>> I want to take the length of a shared array, but `bytevector-length'
>> throws an error claiming the shared array isn't a bytevector, even
>> though it prints the error argument as one.
>> 
>> I am using Guile 2.0.11, Debian Stable package 2.0.11+1-9.
>
> This is addressed in 2.1, by
> eb3d623da57e6d31a58d95f932345fb761f9b701. Your example will print
> #1vu8(0 0 ...) to signify that it's not a bytevector. You can use
> array-length here.

Thank you.

I didn't realize shared arrays are not bytevectors anymore and wrongly
assumed bytevector procedures could be applied to arrays, even tho array
procedures can be applied to bytevectors.

Re: `bytevector-length' doesn't accept a shared array from a bytevector

[Daniel Llorens]

On 21 Feb 2017, at 19:51, Diogo F. S. Ramos <dfsr@riseup.net> wrote:

>> On 21 Feb 2017, at 14:21, Diogo F. S. Ramos <dfsr@riseup.net> wrote:
>> 
>>> I want to take the length of a shared array, but `bytevector-length'
>>> throws an error claiming the shared array isn't a bytevector, even
>>> though it prints the error argument as one.
>>> 
>>> I am using Guile 2.0.11, Debian Stable package 2.0.11+1-9.
>> 
>> This is addressed in 2.1, by
>> eb3d623da57e6d31a58d95f932345fb761f9b701. Your example will print
>> #1vu8(0 0 ...) to signify that it's not a bytevector. You can use
>> array-length here.
> 
> Thank you.
> 
> I didn't realize shared arrays are not bytevectors anymore and wrongly
> assumed bytevector procedures could be applied to arrays, even tho array
> procedures can be applied to bytevectors.

AFAIR bytevector procedures have always failed with actual arrays.

However, the array procedures will return a root vector (a bytevector, an vector, etc.) whenever it's possible for them to do so. E.g. if you change 7 -> 42 in your example, make-shared-array will return a true bytevector. (make-typed-array 'vu8 VALUE LENGTH) will always return a bytevector. Yet another example, typing #1vu8(0 0 ...) in the terminal will print back #vu8(0 0 ...), and it is a true bytevector.

I wouldn't rely on this being true in the future, since I don't think it's documented.