[pro] Default safety level and specialized arrays

[Pascal J. Bourguignon]

> On 10 Mar 2015, at 17:02, Edi Weitz <edi at weitz.de> wrote:
> 
> Hi everybody,
> 
> After rummaging around in the HyperSpec and various implementation
> manuals I came to the following conclusion:
> 
> 1. The standard doesn't prescribe such thing as a default safety level
> for CL implementations and there's no portable way to figure out the
> safety level of the global environment.  (And the same holds for other
> optimize qualities.)  The closest I could find in the CLHS is 3.3.1
> where they talk about an "implementation that always processes code as
> if safety were high."  From this I conclude that implementations are
> allowed NOT to do this or otherwise there would be no need to mention
> it.
> 
> The LispWorks manual for example describes the defaults in section 9.5
> about compiler control, but for SBCL I couldn't find them in the
> manual.
> 
> 2. The standard doesn't prescribe what should happen if you try to
> write an element of a wrong type to a specialized array, even in safe
> code.
> 
> Both LispWorks and SBCL will by default complain in this case but my
> understanding is that you can't rely on this in portable code.
> 
> So, my question is whether the above is correct or if I missed something?


Yes. 

Notably, with (safety 0), Common Lisp implementation could be as good as common C implementations...

This is why it is very bad to put optimization declarations in libraries (well, if they're not (safety 3) (speed 0)): 
it HAS and WILL make users lose days in debugging because YOUR, Edi, libraries, compiled on conforming
implementations fail to detect errors.

-- 
__Pascal J. Bourguignon__



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