On Tuesday, 8 March 2016 at 20:26:04 UTC, Yuxuan Shui wrote:
On Monday, 7 March 2016 at 16:13:45 UTC, Steven Schveighoffer
wrote:
On 3/4/16 4:30 PM, Yuxuan Shui wrote:
On Friday, 4 March 2016 at 15:18:55 UTC, Steven Schveighoffer
wrote:
[...]
Thanks for answering. But I still don't understand why
TypeInfo would
need to be allocated. Aren't typeid() just returning
references to the
__DxxTypeInfo_xxxx__initZ symbol?
You misunderstood, I meant the typeinfo *for* an allocated
object, not that the typeinfo was allocated.
In some cases, 2 different objects allocated from different
libraries (usually DLL-land) may reference TypeInfo from
different segments, even though the TypeInfo is identical.
-Steve
Hmm... Does that mean each DLL will have their own TypeInfo
symbols for the same type?
[Note: I phrase my answer in terms of Linux shared libraries
(*.so) because D doesn't actually have proper Windows DLL support
yet. The same would apply to DLLs, it just feels wrong describing
functionality that doesn't exist.]
They can, mostly due to templated types. Consider modules
`common`, `foo`, and `bar` (all built as shared libraries), and
`main` (built as an executable).
module common; // => common.so
struct List(T)
{
// ...
}
module foo; // => foo.so, links to common.so
import common;
List!int getList()
{
// ...
}
module bar; // => bar.so, links to common.so
import common
void processList(List!int a)
{
// ...
}
module main; // => main, links to foo.so, bar.so, and common.so
import foo, bar;
void main()
{
processList(getList());
}
No part of List!int is instantiated in common, so no part of it
is actually present in common.so. Instead, it is instantiated in
foo and bar, and thus separate copies of List!int are present in
foo.so and bar.so, along with TypeInfo for List!int.
If you were to statically link instead (using .a or .lib files),
the linker would keep only one copy of List!int and its TypeInfo,
but the linker can't eliminate either of them when dealing with
shared libraries.
So, yes, I think the string comparison is needed, as awkward as
it may seem in many circumstances.
