On 28.11.2025 21:14, tzsz wrote:
Hello,
I'd like to ask if there is any way of creating a class instance at a
location given by a pointer.
In C++ this is usually done using new(pointer) MyClass(); and I saw a
post made by Walter Bright that suggested adding this to D. The code
from that post did not compile on my machine tho. And the post was a few
years old, so I don't know what the current state regarding this feature
is. I really tried finding something via Google but I was unsuccessful.
The reason for this is that I am looking for a way to use classes with
all their nice features but without the GC. Therefore I'd be doing all
the (de)allocations on my own. For this, I am currently using malloc and
free from core.stdc.
Kind regards
In C++ it is called placement new. In D you should emplace class:
```D
import core.lifetime : emplace;
import core.stdc.stdlib : malloc, free;
import std.stdio : writeln;
class MyClass
{
int value;
this(int v)
{
value = v;
writeln("MyClass constructor called with value: ", value);
}
~this()
{
writeln("MyClass destructor called for value: ", value);
}
}
void main()
{
// Allocate memory for MyClass
void* rawMemory = malloc(__traits(classInstanceSize, MyClass));
if (!rawMemory)
{
throw new Exception("Out of memory!");
}
// Cast the raw memory to the class type
MyClass instancePtr = cast(MyClass)rawMemory;
// Emplace the MyClass instance
emplace!MyClass(instancePtr, 10);
// Now you can use instancePtr as a regular class instance
writeln("Value from emplaced instance: ", instancePtr.value);
// Remember to manually call the destructor and free the memory for
non-GC allocated objects
destroy(instancePtr);
free(rawMemory);
}
```
