Understanding different types in Fortran

Question

I was reading a Fortran code, came across the following code, couldn't understand what it does.

m%AllOuts( BAzimuth(k) ) = m%BEMT_u(indx)%psi(k)*R2D

I know that % here works like a pipe indicator to access values in a way similar to a dictionary in Python. I have a dictionary m let's say and the first key is AllOuts, but what does anything inside parentheses mean? Is it like another dictionary?

Answer 1

The percent sign is not denoting a dictionary. There are no native dictionaries in Fortran.

The percent sign denotes the component of a type. For example:

! Declare a type
type :: rectangle
    integer :: x, y
    character(len=8) :: color
end type rectangle

! Declare a variable of this type
type(rectangle) :: my_rect

! Use the type

my_rect % x = 4
my_rect % y = 3
my_rect % color = 'red'

print *, "Area: ", my_rect % x * my_rect % y

The parentheses could either indicate the index of an array, or the arguments of a call.

So, for example:

integer, dimension(10) :: a

a(8) = 16     ! write the number 16 to the 8th element of array a

Or, as a prodedure:

print *, my_pow(2, 3)

...

contains

function my_pow(a, b)
    integer, intent(in) :: a, b
    my_pow = a ** b
end function my_pow

In order to figure out what m is, you'd need to look at the declaration of m, which would be something like

type(sometype) :: m

or

class(sometype) :: m

Then you'd need to find out the type declaration, which would be something like

type :: sometype
    ! component declarations in here
end type

Now one of the components, BEMT_u, is almost certainly an array of a different type, which you'd also need to look up.