On 06/22/2012 08:57 PM, Michel Colman wrote:
Isn't this what a do-while loop is for, or am I missing something?
Well, yes, but then you don't need the regular "for" loop either. After
all, isn't that what a "while" loop is for?
The big advantage of "for" is that you can see at a glance what the
initialisation, condition(s) and increments are. It describes the whole
loop in one statement. That's the only reason why it was invented in the
first place, because the language technically does not need it. You can
even declare the variable right there so its scope is limited to the
loop. With a do-while, you first initialize the variable before the loop
(outside of it), then add the increment just before the end (many pages
later, perhaps), and the condition at the very end. It's all over the
place.
foreach(i; 0..10)
I know my simple example would be optimized, and can indeed be written
with a foreach as well. But if you use some custom class as the
variable, or a pointer, it won't be. For example, turn i into a Bigint.
foreach-range works with custom types.
Or for an entirely different example:
for (Display * d = firstDisplay; d != 0; d = nextDisplay)
if you have already established that at least one display is present.
If firstDisplay is trivially non-null, the compiler will remove the
comparison. Furthermore, the additional comparison is extremely cheap
and will likely be completely unnoticeable.
Or even simpler:
for (int i = 1; i <= 0x10000000; i <<= 1)
I bet this won't be optimized on many compilers.
I bet this is optimized on any halfway decent optimizing compiler. This
is the kind of simple optimization compilers are good at.
And all it would take is one extra semicolon:
for (Display * d = firstDisplay; ; d != 0; d = nextDisplay)
for (int i = 1; ; i <= 0x10000000; i <<= 1)
to tell the compiler to skip the condition before the first iteration.
The examples do not make a compelling case.
