CODEWITHSUNDEEP
oopfortrangeneric-programming
Zeus
Zeus

Reputation: 1525

Fortran OOP Generic

I am getting confused on the difference between using

Procedure :: momentum => particle_momentum

and using

Procedure :: particle_momentum 
generic :: momentum => particle_momentum

Here is a type declaration

type particle

  type(vector) :: position, velocity
  real :: mass

  contains

  procedure :: momentum => particle_momentum
  procedure :: energy => particle_energy

end type particle

Upvotes: 2

Views: 192

Answers (2)

Sorush
Sorush

Reputation: 4129

Simply saying, "generic" is to make life easier, the compiler chooses the suitable form of a procedure among others just by calling a specific command, for example, you want to call the right constructor of an object with "initialize" command. There are some rules should be obeyed the compiler can distinguish them.

On the other hand, "procedure:: x=>y" is employed to override/point one of object procedures (x) to a new function (y).

Upvotes: 0

Vladimir F Героям слава
Vladimir F Героям слава

Reputation: 59998

Procedure :: momentum => particle_momentum

defines a type-bound procedure, similar to virtual procedures in other languages. It is a binding of an existing procedure to perform the role of the type-bound procedure.

They use the dynamic dispatch, i.e., when you call

  class(particle) :: o
  ..
  call o%momentum

it is possible that if the dynamic type of o is en extended type (child) of particle you actually run a procedure that overrides particle_momentum. You don't know if you actually call the original, or the overriding procedure, until run-time.

Now suppose you have

procedure :: particle_momentum_int
procedure :: particle_momentum_real
generic :: momentum => particle_momentum_int, particle_momentum_real

as

subroutine particle_momentum_real(self, a)
   class(particle) :: self
   real :: a

subroutine particle_momentum_int(self, a)
   class(particle) :: self
   integer :: a

Then if you call

class(particle) :: o !or just type(o)
..
call o%momentum(1)

you know that you call the _int variant by the rules of generic disambiguation and you know it at the compile-time. This is the static dispatch.

Upvotes: 3

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