Error compiling - "Assignment to reference" - in Cython 0.18

[Czarek Tomczak]

Hi there,

I've upgraded to from Cython 0.17.4 to Cython 0.18 and I'm getting this

error message while compiling:

    request_handler.pyx:147:32: Assignment to reference 'cefAllowOSExecution'

The code is as follows:

    from libcpp cimport bool as cpp_bool

    cdef public cpp_bool RequestHandler_OnProtocolExecution(

            CefRefPtr[CefBrowser] cefBrowser,

            CefString& cefUrl,

            cpp_bool& cefAllowOSExecution

            ) except * with gil:

        cefAllowOSExecution = bool(pyAllowOSExecution[0])

It worked fine in Cython 0.17, how do I make it work in Cython 0.18? I've tried 

google but no luck.

Thanks for help,

Czarek

[Gerald Dalley]

I'm seeing this problem in Cython 0.19 too.

[Robert Bradshaw]

I'm curious how this ever worked. In any case, there's no reason to
pass a bool as a ref, and certainly not if you're going to re-assign
it before even looking at it (which I assume is an artifact of being a
trimmed-down example).

- Robert

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[Czarek Tomczak]

I'm depending on a library that uses this style of references, I'm not

sure how to go around this, I'm stuck with Cython 0.17.4 it seems.

Yes, that was a trimmed-down example.

Regards,

Czarek

[Gerald Dalley]

In my case, I have a pure Cython cdef function that works like this:

    cdef int memo_key = 0

    cdef map[int,int] memoized_result

    

    cdef foo(int key, map[int,int]& result):

        # NOT threadsafe or re-entrant

        if key != memo_key:

            memoized_result.clear()

            ...populate memoized_result...

            memo_key = key

        result = memoized_result

The function works fine with Cython 0.17.4: it properly causes map's assignment operator to be invoked.  

With Cython 0.19, the Cython compiler fails with an "Assignment to reference" error.

[Nikita Nemkin]

On Fri, 26 Apr 2013 02:08:06 +0600, Gerald Dalley
<gerald...@gmail.com> wrote:

> On Thursday, April 25, 2013 3:54:45 PM UTC-4, Czarek Tomczak wrote:
>>
>> I'm depending on a library that uses this style of references, I'm not
>> sure how to go around this, I'm stuck with Cython 0.17.4 it seems.
>> Yes, that was a trimmed-down example.

A simple (and ugly) workaround for reference assignment:

cdef void test(int& out):
(&out)[0] = 123

>> On Thursday, April 25, 2013 9:47:50 PM UTC+2, Robert Bradshaw wrote:
>>> I'm curious how this ever worked. In any case, there's no reason to
>>> pass a bool as a ref, and certainly not if you're going to re-assign
>>> it before even looking at it (which I assume is an artifact of being a
>>> trimmed-down example).

Using references for output parameters is relatively common in C++,
there is nothing unusual in Czarek's example.


Best regards,
Nikita Nemkin

[Robert Bradshaw]

Oh, yes, of course. Good old C++, where local T& x is unassignable but
assigning to an argument T& x is a common idiom. This is a bug in
Cython.

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[Czarek Tomczak]

Using the "(&out)[0] = " fix for referenced arguments works great.

Thank you so much Nikita for this fix, I can use latest version of

Cython again (it's still not fixed in Cython 0.19.1).

Best regards,

Czarek

[Matthias Kümmerer]

I just stumbled across this bug and noticed that it is still present in Cython 0.23.4. Are there any plans to fix this?

Best regards,

  Matthias

[mahesh ravishankar]

I see this too, and would really like a fix for it. My use case is to be able to pass a reference to a empty memoryview object which is assigned to within the function so that the caller can use the memoryview object