How to provide alternatives in sequence

[Flamefire]

Suppose I have the following class:

struct Foo{
  virtual void before();
  virtual void do();
  virtual void after();
};

With the sequence approach I can make sure, those functions are called in order when having a single instance.

But what do I do when I have multiple instances? Example:

Foo* f1 = new Foo;
Foo* f2 = new Foo;
container.add(f1, f2);
// Expect (f1.before && f2.before) + (f1.do && f2.do)  + (f1.after && f2.after) 
container.process();

How can I ensure, that both before are called first, then both do etc while the order of the calls to the same function do not matter?

[mat007]

You probably need to use several sequences for that, which I admit is a little cumbersome…

Something like:

• s1 : f1.before -> f1.do
• s2 : f1.before -> f2.do
• s3 : f2.before -> f1.do
• s4 : f2.before -> f2.do

etc…