On 2011-08-22 21:27:39 +0000, Stewart Gordon <smjg_1...@yahoo.com> said:
On 20/08/2011 07:28, Bernard Helyer wrote:
On Sat, 20 Aug 2011 01:42:56 +0100, Stewart Gordon wrote:
So essentially you're looking to catch cases where, if you consider the
function as a flow chart, there is no chain of arrows from the start of
the function to the statement in question. That should be
straightforward. But you're not worrying about catching cases where
some arrow would never be followed. Have I got that right?
Pretty much, minor correction on the last part -- an arrow means that the
compiler considers it a possibility, so it's not considered in so far as
the data structure doesn't make the distinction.
That's more or less what I meant. The compiler can't identify all
arrows that will never be followed - this would mean solving the
halting problem. So it takes the view that any arrow _may_ be
followed. But if there's no arrow at all leading to a statement, the
compiler can easily see that it's unreachable and so issue a
warning/error.
But what about templates? Take this pretty reasonable function template:
bool frontEquals(R, V)(R range, V value)
{
if (range.empty)
return false;
else
return range.front == value;
}
This will work fine with most ranges, but if you encounter an infinite
range (with empty defined as "enum empty = false") then the "return
false" statement becomes unreachable and you'll get an error/warning?
It doesn't make sense.
Or perhaps we should require the above to be written like this:
bool frontEquals(R, V)(R range, V value)
{
static if (!range.isInifinite)
if (range.empty)
return false;
return range.front == value;
}
But isn't that messy? And I'm dealing with only one possibility here…
what if a range was always empty? Something else to care about.
Thankfully I'm only checking a boolean property limited to two values.
--
Michel Fortin
michel.for...@michelf.com
http://michelf.com/
