From: Rob Stewart (stewart_at_[hidden])
Date: 2005-03-09 16:40:46
From: Matthew Vogt <mattvogt_at_[hidden]>
> Rob Stewart wrote:
> >>I guess it looks okay with c.value(). What do you think?
> > I don't like it.
> I don't like it either, but it does have the benefit of simplifying the code by
> removing all the explicit good() tests. I think explicit testing for good
> status is something that's going to be very easy to forget, while you're trying
> to write 'simple' filters that are implemented in get functions which can
> (effectively) be called asynchronously.
Your code had implicit goodness tests. They, too, can be
forgotten, but I understand your point is that this:
if (c = get(src))
isn't checking whether c is a non-zero character, but whether it
is a good character.
> > That's the right approach: just code in terms of good(c). You
> > get simplified code without the oddity of asking a
> > basic_character for its character. The real value in the
> > suggestion is that one should ignore fail() and eof()
> > conditions in the filter. That's something you can document and
> > your examples can show the simplified form.
> But the 'simplified' form will have (c = get(src) && c.good()) everywhere, and
> the abstraction of algorithm state will result in more convoluted boolean
> expressions where testing 'good' will be very easy to omit...
I was thinking of "good(c = get(src))" which isn't convoluted.
> >>You'd be relying on the conversion as a substitute for good, no?
> > Syntactic sugar is nice when it isn't too sweet.
> Well, if it helps correctness, it isn't really sugar.
One thing to remember is that a filter is write once, use many
times (modulo bug fixes). Once it works, it works. The
syntactic sugar you're suggesting applies in only a few
expressions in such a filter, so it isn't much of a win, is it?
Let's review. There are several things one needs to do with a
- return it from a function
- test it to determine success
- compare it to a char/wchar_t
Have I missed anything?
Given those requirements the class needs:
- value semantics
- safe-bool conversion
- comparisons with char/wchar_t
Therefore, I think this will work:
template <typename Ch>
Ch value() const;
operator unspecified-bool-type() const;
bool operator ==(Ch const) const;
bool operator !=(Ch const) const;
bool operator >(Ch const) const;
bool operator >=(Ch const) const;
bool operator <(Ch const) const;
bool operator <=(Ch const) const;
friend bool good(basic_character const);
friend bool fail(basic_character const);
friend bool eof(basic_character const);
friend bool would_block(basic_character const);
Now you can write both of these:
if (c = get(src))
if (c == comment_char_)
-- Rob Stewart stewart_at_[hidden] Software Engineer http://www.sig.com Susquehanna International Group, LLP using std::disclaimer;
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