D versus Objective C Comparison

[Michel Fortin]

On 2009-02-02 21:19:52 -0500, Daniel Keep <daniel.keep.lists at gmail.com> 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
michel.fortin at michelf.com
http://michelf.com/