[boost] Re: filesystem portability checks

From: Peter Dimov (pdimov_at_[hidden])
Date: 2004-10-26 14:49:44

Beman Dawes wrote:
> At 02:10 PM 10/25/2004, Peter Dimov wrote:
>
>> ... I certainly wouldn't mind a filesystem
>> _warning_ for nonportable paths, if we find a suitable delivery
> mechanism.
>
> Interesting! A fresh perspective.
>
> Let's see what can be done within the current design. A adaptor
> function could intercept what otherwise would be errors and turn them
> into warnings:
> bool warn_nonportable_name( std::string const & name )
>
> {
>   if ( !fs::portable_name( name ) )
>     boost::issue_warning( "Warning, path contains non-portable name: "
>       + p );
>   return true;
> }
>
> Because the adaptor always returns true, an error exception is never
> thrown. This function could become the new default, or could be
> explicitly coded like any name_check function.

[...]

> Does that capture what you had in mind?

Almost.

The current validation scheme (with the above addition) is (IIUC):

1. Parse path according to grammar, throw on parse error;

2. Check every path element with checker(e), throw on false;

    Warning checker calls issue_warning on nonportable paths.

What I had in mind was more like:

1. Parse path according to grammar, throw on parse error;

2. Call checker(e) for every path element;
    if false, call fs_nonportable_path_element

Where:

void (*fs_nonportable_path_element)( std::string const & path, std::string 
const & element ) = __fsnp_default;

(as an aside, the exceptions really need their own types, because these 
aren't filesystem errors, i.e. no underlying filesystem error code is 
associated with them.)

The general idea of this approach is that if the user wants an exception on 
nonportable path elements, the name checker can simply throw.

If the user wants the current behavior, he can install an 
fs_nonportable_path_element that throws.

Otherwise, he can install an appropriate handler that logs or ignores the 
nonportable path.

It might even be possible to get rid of the default name checker 
"replaceable global constant", if the original default is now good enough 
and nobody needs to change it.