Am 11.05.2015 um 21:39 schrieb Laeeth Isharc:
On Monday, 11 May 2015 at 12:54:09 UTC, Benjamin Thaut wrote:
and why does it not map well to D ?
D uses tons of templates everywhere. Even type information for non
templated types is generated on demand and stored in comdats which can
lead to duplicate symbols the same way it does for templates. In D the
dynamic cast is basically the default and you have to force the
compiler to not use a dynamic cast if you care for performance.
Sorry for the rookie question, but my background is C rather than C++.
How do I force a static cast, and roughly order magnitude how big is the
cost of a dynamic cast ?
Would you mean for example rather than casting a char[] to a string
taking the address and casting the pointer?
Dynamic casts only apply to classes. They don't apply to basic types.
Example
object o = instance;
SomeClass c = cast(SomeClass)instance; // dynamic cast, checks type info
SomeClass c2 = cast(SomeClass)cast(void*)instance; // unsafe cast,
simply assumes instance is SomeClass
If you do the cast in a tight loop it can have quite some performance
impact because it walks the type info chain. Walking the type info
hirarchy may cause multiple cache misses and thus a significant
performance impact. The unsafe cast literally does not anything besides
copying the pointer.
