Modern Fortran Development

This skill covers writing modern, maintainable Fortran (2003/2008 and later) for scientific and numerical computing, including module organization, kind parameters, procedure design, memory safety, and testing.

Workflow for Writing a Modern Fortran Module

1. Define shared kinds first — Create a kinds_mod (or similarly named) module with iso_fortran_env or selected_real_kind/selected_int_kind parameters used across the whole project.
2. Design the module — Group related derived types and procedures into one focused module per file; declare implicit none at the top.
3. Write procedure interfaces — Give every dummy argument an explicit intent(in), intent(out), or intent(inout); use use, only: to import exactly what's needed.
4. Implement with early validation — Check preconditions (array bounds, allocation state, valid ranges) at the top of each procedure and return/stop early rather than nesting deeply.
5. Manage arrays explicitly — Use allocatable arrays, check allocated() before use, and deallocate when the lifetime isn't naturally scoped.
6. Build with warnings on — Compile with -Wall -Wextra -std=f2008 (gfortran) or the equivalent, and fail CI on new warnings.
7. Test — Write unit tests for individual procedures and integration tests for full numerical workflows, checking tolerances rather than exact floating-point equality.

Basic Principles