Re: find-file-noselect needs save-match-data

[Herbert Euler]

> > It's quite the opposite IMO.  "safe" can mean many things, whereas
> > "nodata" clearly indicates that it doesn't set (or modify) match-data.
>
> "-nodata" is good.
>
> > But in practice, we should have a macro to encapsulate calls:
> >
> >     (preserve-match-data (string-match ...))
>
> This would violate referential transparency.  Consider
>
> (defvar foobar "foobar")
>
> (defun foo ()
>   (string-match "foo" foobar)
>   (match-string 0 foobar))
>
> (defun bar ()
>   (string-match "bar" foobar)
>   (preserve-match-data
>    (foo)))

Since most applications do not use the match data in practice, I think
if an application use the match data, it should require it explicitly.
I.e., please take a look at the following:

   ;; Normal applications (no use of match data).
   (if (string-match "foo" bar)
       ;; True branch.
     ;; False branch.)
   (foo-bar)

   ;; Applications that use match-data.
   (if (string-match "foo" bar)
       (with-match-data (match-data)
         ;; True branch.)
     ;; No need to use `with-match-data' here, since there is no
     ;; match data.
     ;; False branch.)
   (foo-bar)

IMO, if we can adapt to this model easily, we can make least changes
to existing code.

Regards,
Guanpeng Xu

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