• Tomer Filiba (24/24) Mar 28 2016 In continuation of an ancient thread:
• Adam D. Ruppe (8/16) Mar 28 2016 eeek, plain `cast(Object) obj` works for this! You don't need all
• Tomer Filiba (7/11) Mar 28 2016 yes, but it's used for logging exceptions. instead of doing the
• Adam D. Ruppe (11/15) Mar 28 2016 Perhaps you can set your own trace handler and either copy/paste

Tomer Filiba <tomerfiliba gmail.com> writes:

In continuation of an ancient thread: 
http://forum.dlang.org/post/k9gu6d$2glr$1 digitalmars.com

I wanted to do something like what Gor wanted, ended up with this:

Object interfaceToObject(I)(I obj) if (is(I == interface)) {
     import object;
     return cast(Object)(cast(void*)obj - 
((cast(Interface*)obj.__vptr[0]).offset));
}

writeln(interfaceToObject(ex.info))
// prints core.runtime.defaultTraceHandler.DefaultTraceInfo

By the way, the reason I need it is to get the actual callstack 
from the TraceInfo, so in reality it's much worse:

struct DefaultTraceInfo {
     int      numframes;
     void*[0] callstack;
}
auto traceInfo = 
cast(DefaultTraceInfo*)(cast(void*)(interfaceToObject(ex.info)) + 
(void*).sizeof * 2);

It would be really nice if TraceInfo exposed the callstack to the 
user. It only provides an opApply that converts to it string... 
adding a simple property such as

 property void*[] frames();

would be awesome.

Adam D. Ruppe <destructionator gmail.com> writes:

On Monday, 28 March 2016 at 11:58:17 UTC, Tomer Filiba wrote:
 Object interfaceToObject(I)(I obj) if (is(I == interface)) {
     import object;
     return cast(Object)(cast(void*)obj - 
 ((cast(Interface*)obj.__vptr[0]).offset));
 }

eeek, plain `cast(Object) obj` works for this! You don't need all 
that other stuff.

 It would be really nice if TraceInfo exposed the callstack to 
 the user. It only provides an opApply that converts to it 
 string... adding a simple property such as

You could always call the backtrace function from the debug info 
if you are on Linux.

http://man7.org/linux/man-pages/man3/backtrace.3.html

That's what trace info used to do. (now it does it itself but 
same thing)

Tomer Filiba <tomerfiliba gmail.com> writes:

On Monday, 28 March 2016 at 14:31:57 UTC, Adam D. Ruppe wrote:
 eeek, plain `cast(Object) obj` works for this! You don't need 
 all that other stuff.

cool! didn't know that. it makes sense now that i think of it.

 You could always call the backtrace function from the debug 
 info if you are on Linux.

yes, but it's used for logging exceptions. instead of doing the 
to-string conversion in place, we just keep the raw pointers and 
do addr2line on demand. so we're given an exception and need to 
extract the bt from it

-tomer

Adam D. Ruppe <destructionator gmail.com> writes:

On Monday, 28 March 2016 at 17:40:15 UTC, Tomer Filiba wrote:
 yes, but it's used for logging exceptions. instead of doing the 
 to-string conversion in place, we just keep the raw pointers 
 and do addr2line on demand. so we're given an exception and 
 need to extract the bt from it

Perhaps you can set your own trace handler and either copy/paste 
code from druntime or just do your own backtrace() based thing:

http://dpldocs.info/experimental-docs/core.runtime.Runtime.traceHandler.1.html


Ugh, the druntime authors didn't actually document TraceHandler 
(it is listed as private, but that function obviously isn't). It 
is:

     alias Throwable.TraceInfo function( void* ptr ) TraceHandler;


The thing it passes is typically null. So you construct your own 
class fitting the TraceInfo interface and this is called when an 
exception is built.