Nick Sabalausky wrote:
"Michel Fortin" <[email protected]> wrote in message
news:[email protected]...
On 2009-02-02 21:19:52 -0500, Daniel Keep <[email protected]>
said:
Michel Fortin wrote:
[stuff]
Wouldn't this be just as well served with Walter's "universal function
syntax"; ie:
void backup(File this, string backupPath)
{
copy(this.path, backupPath ~ "/" ~ this.name);
}
File someFile;
someFile.backup(backupPath);
It would work in your example, but not in mine. Note the difference:
foreach(child; children)
child.backup(backupPath ~ "/" ~ this.name);
Statically, child is a Node here. If at runtime child is a File, the
backup function is overriden by the FileBackup extension of File, so it'd
call the backup function from FileBackup, not NodeBackup. If at runtime
child is a Directory, it'll call DirectoryBackup's backup function. At
least, that's what it would do in Objective-C using categories. And that's
why you don't need the visitor pattern in Objective-C.
--
Michel Fortin
[email protected]
http://michelf.com/
I had been slowly coming around to the idea of having that universal
function syntax instead of C#-style explicit extension methods, but maybe
this need for dynamic dispatch is a good reason to prefer explicit extension
methods:
[snip]
I think that allowing interfaces to be declared AFTER the objects which
satify them, would be a more general solution.
Create a vtable, fill it with all the entries from the object's vtable,
and add any extra functions you want.
Then you could allow structs to support interfaces, for example.
