• Bruce Adams <tortoise_74 yeah.who.co.uk> Oct 29 2007

Bruce Adams <tortoise_74 yeah.who.co.uk> writes:

TomD Wrote:

 Walter Bright Wrote:
 
 An interesting and sometimes amusing read:
 
 http://yosefk.com/c++fqa/


 
 But I wonder if the following is also true for D:
 ----snip---
 [10.1] What's the deal with constructors?
 
 FAQ: A constructor initializes an object given a chunk of memory having
arbitrary (undefined) state, the way "init functions" do. It may acquire
resource like memory, files, etc. "Ctor" is a common abbreviation.
 
 FQA: That's right - constructors initialize objects. In particular,
constructors don't allocate the chunk of memory used for storing the object.
This is done by the code calling a constructor.
 
 The compiler thus has to know the size of a memory chunk needed to store an
object of a class (this is the value substituted for sizeof(MyClass)) at each
point where the class is used. That means knowing all members (public &
private). This is a key reason why changing the private parts of a C++ class
definition requires recompilation of all calling code, effectively making the
private members a part of the public interface. 
 
 ---snap---
 
 Given the compilation speed of DMD, it does not bother me, but still, he
 has a point here.
 
 Ciao
 Tom


I have been bothered by that for many years. I had an idea to implement truly
opaque types by having the size of the object used as a link time variable. If
I recall it wasn't possible using the ELF binary format. I think I ended up
using code generation and the PIMPL idiom instead. However, D is not
constrained to use an existing object format itself only for its C/C++
interface. 

Regards,

Bruce.