Re: [GD-General] Eiffel

[Thatcher U. <tu...@tu...>]

On Sun, 23 Dec 2001, Jesse Jones wrote:

> At 11:47 PM -0500 12/22/01, Thatcher Ulrich wrote:
>
> >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

No, that's not the same test --  I want to check the value as well.  I
don't think it's possible to  do w/ STL without either explicity using
an iterator, or doing two lookups.

> >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.

It's a leak -- if my_hash[my_key] is not defined, then it allocates
memory and there's no way to safely clean it up.  The above code is
bugged, end of story.

-Thatcher