On 01/03/2012 12:07 PM, Jonathan M Davis wrote:
On Tuesday, January 03, 2012 11:52:13 Matej Nanut wrote:
Hello everyone,
I would like to know whether
if (symbol in symbols)
return symbols[symbol];
is any less efficient than
auto tmp = symbol in symbols;
if (tmp !is null)
return *tmp;
Without optimisation, it looks like the first example
searches for `symbol' twice.
Of course it does. in does a search and returns a pointer to the element in
the AA (or null if it isn't there). The subscript operator also does a search,
returning the element if it's there and blowing up if it's not
(OutOfRangeError IIRC without -release and who-knows-what with -release). So,
if you use in and then the subscript operator, of course it's going to search
twice. Part of the point of using in is to not have to do a double lookup
(like you would be doing if AAs had a contains function and you called that
prior to using the substript operator).
The correct way to do it is the second way, though you should be able to
reduce it to
if(auto tmp = symbol in symbols)
return *tmp;
- Jonathan M Davis
I think this is the single most ugly thing in the language. IIRC ldc
will generate identical code for both code snippets.
