[Issue 4483] New: Make foreach over string or wstring where element type not specified a warning

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=4483

           Summary: Make foreach over string or wstring where element type
                    not specified a warning
           Product: D
           Version: D2
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: jmdavisProg at gmail.com


--- Comment #0 from Jonathan M Davis <jmdavisProg at gmail.com> 2010-07-18 07:43:26 PDT ---
Strings are dealt with fantastically in D overall, but the very nature of UTF-8
and UTF-16 makes it easy to screw things up when trying to deal with individual
characters. In foreach loops, D can convert the chars or wchars to dchar and
avoid the problem.

foreach(dchar c; str)

However, if you fail to give an element type

foreach(c; str)

then the element type will be the element type of the array. Normally this is
good, but for strings, wstrings, char[], and wchar[] this is generally _bad_.
In most cases, what people will likely want is to loop over each code point
rather than each code unit - that is, what they really should be using is

foreach(dchar c; str)

But if they fail to put the element type, that's not what they'll get. So, I
propose that it become a warning whenever someone tries to loop over a char[],
wchar[], string, or wstring without giving the element type. That way, the
programmer will realize that they should have put dchar, since that's almost
certainly what they wanted. If, however, they really did want char or wchar,
then they're free to put that as the element type and iterate normally. But
because iterating over the chars or wchars is almost certainly _not_ what the
programmer wants in almost all cases, it seems to me that it would be
worthwhile to give a warning in cases where they fail to put the element type.
It doesn't restrict the programmer any, but it will help them avoid bugs with
regards to the UTF-8 and UTF-16 encodings.

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