Is there a way to run a class's c'tor on a block of memory from a template function?  For example:

C newClass(C, CtorArgs...)(CtorArgs args) {
    // Allocate, initialize.
    // Want to call the c'tor that takes type CtorArgs.
}

dsimcha wrote:
> Is there a way to run a class's c'tor on a block of memory from a template
> function?  For example:
> 
> C newClass(C, CtorArgs...)(CtorArgs args) {
>     // Allocate, initialize.
>     // Want to call the c'tor that takes type CtorArgs.
> }

----
C newClass(C, CtorArgs...)(CtorArgs args) {
    return new C(args);
}

class Foo{ this(int a, string b) { /* do something */ } }

auto foo = newClass!(Foo)(1, "bar");
----

That seems to work here... or are you meaning you already have a block of memory allocated and want to turn it into an instance of the class? In which case something like:

----
C newClass(C, CtorArgs...)(CtorArgs args) {
   void* mem;
   // Allocate/initialize etc, store in inst of type C
   // Stolen/adapted from Object.d:
   if( inst.classinfo.flags & 8 && inst.classinfo.defaultConstructor )
   {
       C delegate(CtorArgs) ctor;
       ctor.ptr = cast(void*)inst;
       ctor.funcptr = cast(C function(CtorArgs))
                          inst.classinfo.defaultConstructor;
       return ctor(args);
   }
   return null;
}
----

Should work (untested).

== Quote from Robert Clipsham (robert@octarineparrot.com)'s article
> dsimcha wrote:
> > Is there a way to run a class's c'tor on a block of memory from a template function?  For example:
> >
> > C newClass(C, CtorArgs...)(CtorArgs args) {
> >     // Allocate, initialize.
> >     // Want to call the c'tor that takes type CtorArgs.
> > }
> ----
> C newClass(C, CtorArgs...)(CtorArgs args) {
>      return new C(args);
> }
> class Foo{ this(int a, string b) { /* do something */ } }
> auto foo = newClass!(Foo)(1, "bar");
> ----
> That seems to work here... or are you meaning you already have a block of memory allocated and want to turn it into an instance of the class? In which case something like:
> ----
> C newClass(C, CtorArgs...)(CtorArgs args) {
>     void* mem;
>     // Allocate/initialize etc, store in inst of type C
>     // Stolen/adapted from Object.d:
>     if( inst.classinfo.flags & 8 && inst.classinfo.defaultConstructor )
>     {
>         C delegate(CtorArgs) ctor;
>         ctor.ptr = cast(void*)inst;
>         ctor.funcptr = cast(C function(CtorArgs))
>                            inst.classinfo.defaultConstructor;
>         return ctor(args);
>     }
>     return null;
> }
> ----
> Should work (untested).

I meant the latter, but not just for the default constructor, for any constructor.

dsimcha wrote:
> Is there a way to run a class's c'tor on a block of memory from a template
> function?  For example:
> 
> C newClass(C, CtorArgs...)(CtorArgs args) {
>     // Allocate, initialize.
>     // Want to call the c'tor that takes type CtorArgs.
> }

Deeply hidden on the Digitalmars homepage, it hints _ctor() and shows how to correctly construct an object (if you're using dmd):
http://www.digitalmars.com/techtips/class_objects.html

dsimcha wrote:
> == Quote from Robert Clipsham (robert@octarineparrot.com)'s article
>> dsimcha wrote:
>>> Is there a way to run a class's c'tor on a block of memory from a template
>>> function?  For example:
>>>
>>> C newClass(C, CtorArgs...)(CtorArgs args) {
>>>     // Allocate, initialize.
>>>     // Want to call the c'tor that takes type CtorArgs.
>>> }
>> ----
>> C newClass(C, CtorArgs...)(CtorArgs args) {
>>      return new C(args);
>> }
>> class Foo{ this(int a, string b) { /* do something */ } }
>> auto foo = newClass!(Foo)(1, "bar");
>> ----
>> That seems to work here... or are you meaning you already have a block
>> of memory allocated and want to turn it into an instance of the class?
>> In which case something like:
>> ----
>> C newClass(C, CtorArgs...)(CtorArgs args) {
>>     void* mem;
>>     // Allocate/initialize etc, store in inst of type C
>>     // Stolen/adapted from Object.d:
>>     if( inst.classinfo.flags & 8 && inst.classinfo.defaultConstructor )
>>     {
>>         C delegate(CtorArgs) ctor;
>>         ctor.ptr = cast(void*)inst;
>>         ctor.funcptr = cast(C function(CtorArgs))
>>                            inst.classinfo.defaultConstructor;
>>         return ctor(args);
>>     }
>>     return null;
>> }
>> ----
>> Should work (untested).
> 
> I meant the latter, but not just for the default constructor, for any constructor.

I'm not sure that it's possible to access ctors other than the default one, I can't seem to find any mention of them in the abi or object.d, you might have better luck if you search yourself though, I only had a quick skim. If not it might be worth a feature request?

== Quote from grauzone (none@example.net)'s article
> dsimcha wrote:
> > Is there a way to run a class's c'tor on a block of memory from a template function?  For example:
> >
> > C newClass(C, CtorArgs...)(CtorArgs args) {
> >     // Allocate, initialize.
> >     // Want to call the c'tor that takes type CtorArgs.
> > }
> Deeply hidden on the Digitalmars homepage, it hints _ctor() and shows
> how to correctly construct an object (if you're using dmd):
> http://www.digitalmars.com/techtips/class_objects.html

Yeah, I had thought of this, but apparently it doesn't work anymore.  This is called excessive encapsulation--making things so opaque that, when someone really knows what they're doing and has a good reason to mess around with the internals, they still can't.  I'll file an enhancement requesting that this be put back.

== Quote from dsimcha (dsimcha@yahoo.com)'s article
> == Quote from grauzone (none@example.net)'s article
> > dsimcha wrote:
> > > Is there a way to run a class's c'tor on a block of memory from a template function?  For example:
> > >
> > > C newClass(C, CtorArgs...)(CtorArgs args) {
> > >     // Allocate, initialize.
> > >     // Want to call the c'tor that takes type CtorArgs.
> > > }
> > Deeply hidden on the Digitalmars homepage, it hints _ctor() and shows
> > how to correctly construct an object (if you're using dmd):
> > http://www.digitalmars.com/techtips/class_objects.html
> Yeah, I had thought of this, but apparently it doesn't work anymore.  This is called excessive encapsulation--making things so opaque that, when someone really knows what they're doing and has a good reason to mess around with the internals, they still can't.  I'll file an enhancement requesting that this be put back.

Never mind, I realized I was doing two things wrong:

1.  It changed from _ctor to __ctor.
2.  The class needs to define a c'tor  If it doesn't, then there's no default
__ctor() that takes no args.  However, this is easy to check for in a static if
statement.

dsimcha wrote:
> Is there a way to run a class's c'tor on a block of memory from a template
> function?  For example:
> 
> C newClass(C, CtorArgs...)(CtorArgs args) {
>     // Allocate, initialize.
>     // Want to call the c'tor that takes type CtorArgs.
> }

After reading the ticket you made, I was wondering if what you were looking for was:

http://www.digitalmars.com/d/1.0/class.html#allocators
http://www.digitalmars.com/d/1.0/class.html#deallocators

This allows you to use a custom allocator/deallocator and not worry about calling the correct ctor/dtor. If you want to change it for all classes, have a look at the _d_allocclass (or _d_newclass depending on your compiler/runtime) function in the runtime. If you change this you will need to recompile the runtime and it won't work for anyone else unless they use your modified runtime.

== Quote from Robert Clipsham (robert@octarineparrot.com)'s article
> dsimcha wrote:
> > Is there a way to run a class's c'tor on a block of memory from a template function?  For example:
> >
> > C newClass(C, CtorArgs...)(CtorArgs args) {
> >     // Allocate, initialize.
> >     // Want to call the c'tor that takes type CtorArgs.
> > }
> After reading the ticket you made, I was wondering if what you were
> looking for was:
> http://www.digitalmars.com/d/1.0/class.html#allocators
> http://www.digitalmars.com/d/1.0/class.html#deallocators
> This allows you to use a custom allocator/deallocator and not worry
> about calling the correct ctor/dtor. If you want to change it for all
> classes, have a look at the _d_allocclass (or _d_newclass depending on
> your compiler/runtime) function in the runtime. If you change this you
> will need to recompile the runtime and it won't work for anyone else
> unless they use your modified runtime.

Yes, but...

Unless I hack the compiler, only *runtime* type info gets passed to this function.
 I need *compile time* type info so it can be passed to templates to generate/get
the bit mask for the type for my precise heap scanning scheme.

dsimcha wrote:
> == Quote from dsimcha (dsimcha@yahoo.com)'s article
>> == Quote from grauzone (none@example.net)'s article
>>> dsimcha wrote:
>>>> Is there a way to run a class's c'tor on a block of memory from a template
>>>> function?  For example:
>>>>
>>>> C newClass(C, CtorArgs...)(CtorArgs args) {
>>>>     // Allocate, initialize.
>>>>     // Want to call the c'tor that takes type CtorArgs.
>>>> }
>>> Deeply hidden on the Digitalmars homepage, it hints _ctor() and shows
>>> how to correctly construct an object (if you're using dmd):
>>> http://www.digitalmars.com/techtips/class_objects.html
>> Yeah, I had thought of this, but apparently it doesn't work anymore.  This is
>> called excessive encapsulation--making things so opaque that, when someone really
>> knows what they're doing and has a good reason to mess around with the internals,
>> they still can't.  I'll file an enhancement requesting that this be put back.
> 
> Never mind, I realized I was doing two things wrong:
> 
> 1.  It changed from _ctor to __ctor.
> 2.  The class needs to define a c'tor  If it doesn't, then there's no default
> __ctor() that takes no args.  However, this is easy to check for in a static if
> statement.

Walter and I talked a few times about the necessity of providing useful functions a la C++'s placement new in Phobos. std.algorithm offers swap and move, but we need some more. Please advise.

Andrei