On 8/18/15 7:02 AM, Johannes Pfau wrote:
Am Tue, 18 Aug 2015 09:10:25 +0000
schrieb "Marc Schütz" <[email protected]>:
On Monday, 17 August 2015 at 22:34:36 UTC, Andrei Alexandrescu
wrote:
On 8/17/15 2:51 PM, deadalnix wrote:
From the compiler perspective, the tag is much nicer.
Compiler can use
jump table for instance.
The pointer is a more direct conduit to a jump table.
Not really, because it most likely doesn't point to where you
need it, but to a `TypeInfo` struct instead, which doesn't help
you in a `switch` statement. Besides, you probably shouldn't
compare pointers vs integers, but pointers vs enums.
Here's an example with an enum tag, showing what compilers can do:
http://goo.gl/NUZwNo
ARM ASM is easier to read for me. Feel free to switch to X86.
The jump table requires only one instruction (the cmp #4 shouldn't be
necessary for a final switch, probably a GDC/GCC enhancement). All
instructions/data should be in the instruction cache. There's no
register save / function call overhead.
If you use a pointer:
http://goo.gl/9kb0vQ
That's a language issue - switch does not work with any pointers. I just
submitted https://issues.dlang.org/show_bug.cgi?id=14931. -- Andrei
