Bill Baxter wrote:
On Wed, Dec 31, 2008 at 4:32 AM, Andrei Alexandrescu
<seewebsiteforem...@erdani.org> wrote:
Don wrote:
Andrei Alexandrescu wrote:
Don wrote:
Christopher Wright wrote:
Don wrote:
The creation of temporaries during expressions is something I'm
currently working on solving. The case you mentioned is addressed by a
proposal I made long ago:
The easiest way is to add an intermediate struct. This takes a fair bit
of manual effort, though, and prevents you from using auto.
That particular case is the easiest possible one. The case x = y - x,
for example, is much more difficult to recognize.
Essentially, you need a struct MyClassAddition that just records
operands. Then give it an implicit cast to MyClass that does the work. This
is an ugly solution because you need to duplicate the operator overloads on
MyClassXXX as well as MyClass.
I believe I got this solution from an article by Andrei. It should work
pretty well for classes that define few overloads.
I'm talking about a language solution. I want to solve this for the
general case.
Don't forget that the case you are solving is not general enough because
you are focusing on eliminating temporaries, which is only part of the
story. I suggest you make place in your thoughts for loop fusion.
Yes. That's the classic problem for matrices, but I'm still trying to work
out if it is really a general problem. I was hoping to see some new use
cases, but none so far.
I think the matrices case is important enough to make it its own class of
problems. For example, bitmap processing is another instance of matrix
usefulness, just one that doesn't usually jump to mind when thinking of
matrices.
Graph algorithms can often be thought of as matrices too.
I recall some shortest path algorithms where you write edge weight
between node i & j in the i,j entry. Then you do a multiply on the
matrices, but instead of using the regular vector inner product for
each <row, column>, you use max(). I forget which algo it is. I'm
thinking Floyd-Warshall. Also there was some algorithm I recall that
can be done with a boolean matrix. Probably some kind of connected
components algo?
--bb
Any graph algorithm that uses e.g. the adjacency matrix... well, uses a
matrix :o).
Andrei
