On 01/03/2012 12:22 PM, Jonathan M Davis wrote:
On Tuesday, January 03, 2012 12:13:45 Timon Gehr wrote:
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.
What, declaring variables in if statements? It's fantastic IMHO. It allows you
to restrict the scope of the variable to the if statement's scope and still
use it in the if's condition. And yes, as far as the assembly goes, the
generated code is identical. But the scoping for the variable is most
definitely different - it won't exist past the if statement if it's declared in
the if's condition - and it saves you a line of code. The reduced scope is the
more important of the two though IMHO, as nice as saving a line of code is.
- Jonathan M Davis
No, I love declaring variables in if statements and would like it to be
extended to while statements as well. What I meant is the fact that
something called 'in' returns a pointer. And the two code snippets I was
referring to were the two in Matej's post.
