Re: [GD-General] Eiffel

[Jesse J. <jes...@mi...>]

At 11:47 PM -0500 12/22/01, Thatcher Ulrich wrote:
>On Sat, 22 Dec 2001, Jesse Jones wrote:
>  > It allows you to write code like this:
>>
>>  Editor* editor = ...;
>>  boldButton->SetCallback(boost::bind(&Editor::SetStyle, editor,
>>  kBold));
>>
>>  italicButton->SetCallback(boost::bind(&Editor::SetStyle,
>  > editor, kItalic));
>
>That's nice, but I don't think that addresses Kent's complaint.

Like I said, it's not a replacement for closures.

>Let's
>say you wanted to toggle the bold mode on boldButton.callback; how
>would you write:
>
>	struct anon {
>		static Editor* editor;
>		anon(Editor* e) : editor(e) {}
>		static void callback() {
>			int	s = editor->GetStyle();
>			s ^= kBold;
>			editor->SetStyle(s);
>		}
>	} instance(editor);
>	boldButton->SetCallback(instance::callback);
>
>I'm not claiming that's great (in fact it stinks :).

You can't write it inline like Kent wants to (although you might be 
able to with the lambda library). In general I think the best 
approach is to put the logic in a member function and have the 
callback call that.

>An example of how the STL is not "really easy to use":
>
>	std::hash_map<string, int> my_hash;
>
>	...
>	string	my_key = something...;
>	int	my_value = something...;
>
>	// I want to see if my_key is in my_hash, and if so, whether
>	// its value matches my_value.
>	std::hash_map<string, int>::iterator it = my_hash.find(my_key);
>	if (it != my_hash.end() && (*it).second == my_value)
>	{
>		// Match.
>	} else {
>		// Mismatch.
>	}

Try:
    if (my_hash.count(my_key) > 0)
       // match
    else
       // mismatch

>I think I got that right.  The iterator is just obfuscation.  Whereas
>the way you'd do it in Perl or Lua, the seemingly obvious:
>
>	if (my_hash[my_key] == my_value) {
>		// Match.
>	} else {
>		// Mismatch.
>	}
>
>compiles, and leaks memory!

Compiles, but shouldn't leak memory.

>  I've seen code like the above, written by
>professional C++ coders.  I probably wrote code like that myself the
>first half-dozen times I used map or hash_map.  A hash container
>should not define operator[] the way std::hash_map does; it's just
>programmer abuse.

It's not the way I would have written it, but calling it programmer 
abuse is way too strong.

>I find that kind of thing is endemic to the STL.  The STL was designed
>(cleverly) as a demonstration of generic programming, rather than as a
>nice container library.
>Unfortunately, people use it as a container
>library, and IMO it stinks for that.

It's far better than any other container library I've seen...

   -- Jesse