"Steven Schveighoffer" <schvei...@yahoo.com> wrote in message
news:op.u4hhjisgeav...@localhost.localdomain...
> On Sat, 05 Dec 2009 16:08:00 -0500, Nick Sabalausky <a...@a.a> wrote:
>
>> I just noticed in D1 that the values for the cases in a switch must be
>> known
>> at compile-time (btw, the docs don't seem somewhat vague on that). Is
>> this
>> also true in D2? If so, I don't suppose we could get that changed before
>> the
>> book? It's a real PITA for dynamic code.
>
> you mean a real PITA to use if instead of switch?
For long "if else(x == y)" chains where the x is always the same? Yes,
absolutely.
> AFAIK, switch is the way it is to foster different optimizations by the
> compiler.
If the only reason for switch were optimization, then switch would be
useless because it would be easy for the compiler to detect:
if(x == constVal1) {}
else if(x == constVal2) {}
// Etc
And do the exact same optimizations.
> I don't know if optimizations can be performed if the cases are dynamic.
Compared to the if-else chains? Probably not. But so what?
> Also, what happens if two of the cases are dynamically the same?
Switch is a shorthand for a certain pattern of if-else chains, as such, it
should behave the same by choosing the first and skipping the rest.
> I think one of the optimizations is that the compiler can reorder the
> cases to make the testing more streamlined.
>
Ok, so it just won't do that with non-constant cases.
