[Cython] broken array declarators when size is an expression

[Dag Sverre Seljebotn]

Robert Bradshaw wrote:
> On Nov 15, 2008, at 12:14 AM, Stefan Behnel wrote:
>
>   
>> Hi,
>>
>> Lisandro Dalcin wrote:
>>     
>>> changeset:   1333:34aca76e1b9d
>>> summary:     array size must be set as int, not numeric string
>>>
>>> broke mpi4py and petsc4py, where I use stack-allocated arrays where
>>> the size comes from an (external) enumeration, for example:
>>>
>>> cdef char name[MPI_MAX_OBJECT_NAME+1]
>>>       
>> Sorry for that. The problem is that we don't currently have a way  
>> to say "give
>> me the compile-time result for this subtree, but don't complain if  
>> it's a
>> runtime value". I already needed that in a couple of places when  
>> working on
>> Cython, as it can lead to different code when you know the result  
>> of an
>> expression. I just never got around to implement this.
>>
>> I think it's wrong that compile_time_value() raises a compiler  
>> error. It
>> should rather return the result with a hint if it was determined  
>> completely or
>> if part of it is runtime-determined. Then the caller can decide  
>> what to do
>> with this information.
>>     
>
> This has annoyed me too. http://trac.cython.org/cython_trac/ticket/119
>
>   
Idea: I was thinking of perhaps a transform that ran through the tree 
and replaced anything that is a compile-time expression with its literal 
result, i.e.

DEF a = 4
print a

would be turned into

print 4

by this transform directly (just by calling compile_time_value and 
putting it back into IntNodes and StringNodes, really). So code after 
that transform (which would be run right after parsing) would not call 
compile_time_value at all -- if it is known compile-time, a literal 
exprnode is there (and treated the same way as if a literal was coded in 
by the user), otherwise it is only known runtime. Seems simpler than 
extending the compile_time_value protocol with information about 
"runtime-determined" etc.

Unfortunately I don't have time to do it.

Dag Sverre