Re: [Sbcl-help] string type uncertainty?

[William H. N. <wil...@ai...>]

On Tue, May 06, 2003 at 11:26:34PM +0200, Pascal Bourguignon wrote:
> 
> What declarations are needed to compile this without type uncertainty?
> 
> (DEFUN COPY (SRC FROM-SRC DST FROM-DST LENGTH)
>   (DECLARE (STRING SRC DST) (FIXNUM FROM-SRC FROM-DST LENGTH))
>   (WHILE (< 0 LENGTH)
>     (SETF (CHAR DST FROM-DST) (CHAR SRC FROM-SRC))
>     (INCF FROM-DST)
>     (INCF FROM-SRC)
>     (DECF LENGTH))
>   ) ;;COPY

> ; --> MULTIPLE-VALUE-BIND MULTIPLE-VALUE-CALL 
> ; ==>
> ;   (SB-KERNEL:%DATA-VECTOR-AND-INDEX ARRAY SB-INT:INDEX)
> ; 
> ; note: unable to
> ;         optimize
> ;       due to type uncertainty:
> ;         The first argument is a BASE-STRING, not a SIMPLE-ARRAY.

If you can declare SRC and DST to be SIMPLE-STRING, then the code
can be compiled most efficiently, and the notes should go away.

If you don't *want* SRC and DST to be SIMPLE-STRINGs -- perhaps
because you want FILL-POINTERs or something -- then there may be no
completely satisfactory way to get rid of the optimization note. You
could use SB-EXT:INHIBIT-WARNINGS, but that affects an entire region
of code, not just a particular property of a particular symbol.

> (Typical usage of COPY would be:
>       (let ((dst (make-string 10)))
>          (copy "hello" 0 dst 0 5)
>          (copy "world" 0 dst 5 5)
>          dst)
> )

You might also be able to use the standard operator CL:REPLACE for this.
  (let ((dst (make-string 10)))
    (replace dst "hello")
    (replace dst "world" :start1 5)
    dst)

-- 
William Harold Newman <wil...@ai...>
"Don't you *want* SRC and DST to be SIMPLE-STRINGs? I could compile
it so efficiently. Couldn't you think about it a bit more? It might be
very nice if they could be SIMPLE-STRINGs. It would be efficient."
-- Python, trying to be helpful
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