Construct a temporary object without copying

[metab0t]

In my optimization modeling language, I expose some expression class to Python like

struct Expr{
  ...
  ...
};

expr = Expr(5)
expr += x

What I want is to construct a temporary constraint object when I write expr<=1.0 and avoids copying the expr object while keeping memory safe.

I assume that Constraint contains a pointer to the Expr like

struct Constraint{
  Expr* expr;
  char sense;
  double rhs;
};

Constraint operator<=(const Expr& expr, double rhs){
  return Constraint{&expr, '<', rhs};
}

But the code above seems not memory safe to store the raw pointer directly for the following Python code:

expr = Expr(5)
expr += x
constraint = expr <= 0.0

Is there some good solutions to this problem?

[wjakob]

You can use keep_alive and return value policies to do some of these things, but you have to be very careful to get things right. Please see the documentation.

The safer standard solution is to adopt either STL shared pointers or a custom intrusive reference counting-based approach. Again, both are extensively discussed in the documentation.