How do I :let a global variable in my vimrc in vim9script?

Question

I am trying to change my vimrc to vim9script. For inbuilt fortran help, (:h fortran) we have:

:let fortran_free_source=1

This is giving an error:

E1126: Cannot use :let in Vim9 script

If I remove the let, I am getting:

E492: Not an editor command:    fortran_free_source = 1

How should I update this?

Answer 1

In general you have to declare the variable once using var

vim9script

var fortran_free_source = 1

is the equivalent of:

let s:fortran_free_source=1

After the variable has been declared you can modify it without using let.

vim9script

var fortran_free_source = 1

# I change my mind:
fortran_free_source = 0

But if you want to change a global variable they need not to be declared hence:

vim9script

# Set a global variable:
g:fortran_free_source = 1

is the equivalent of:

" Set a global variable:
let g:fortran_free_source=1