Re: That depends... (Was: Regarding assignment to struct)

On 2025-05-03, Kaz Kylheku <643-408-1753@kylheku.com> wrote:

- some structures cannot be copied; duplicating objects can
  be nontrivial when they manage resources or are sensitive
  to their own address (like have pointers to parts of themselves).
  E.g.  you can't just have a FILE parameter and pass (*stdout) to it.
  Under object-based/oriented programming in C, we usually pass
  around pointers to objects. Treating OOP objects by value requires
  techniques found in C++: you need handlers to be invoked when
  objects are copied ("copy constructors").

Expanding on this point, C++ goes to town with pass-by-value interfaces
involving objects. For instance the std::basic_string template allows
C++ programs to treat dynamic strings as just values to be tossed
around:

   std::string path_combine(std::string dir, std::string name)
   {
      return dir + "/" + name;
   }

C++ experience informs us that you can get away with doing this
with PODs (plain old datatypes---structs with no constructors
or destructors) only to a point. But in C, that's all you have.

You are limited in C by not being able to endow the type with
the brains for what to do when it is copied: like for instance
to share a pointer to some associated data with the new copy,
bumping up a reference count.

That tends to exert "downward pressure" on the technique.

--
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