Defining rules for namespaced modules

[perazz]

Motivation

I'm opening this issue to discuss defining rules for namespaced modules.

Specification

There are quite a few things that need be defined. I've started a base implementation in fpm that should make it easy to change them on the go, but the sooner we get to an agreement the better, so I think this is a good place to discuss.

1. Namespace separator/ namespaced module identifier.

I like the idea of _FPM_ which seems to have no collisions with other fpm functionality and looks like _MOD_ which is basically a namespace separator for module entities. However, simpler options are also possible, e.g., \ or %

2. Default namespace.

I think non-namespaced entities should resolve to a default namespace. I would name it

character(*), parameter :: DEFAULT_NAMESPACE = "default"

This means that both default-namespace and non-namespaced module identifiers would be resolved to the default namespace, e.g.:

_FPM_my_mod_1         ! belongs to the default namespace
default_FPM_my_mod_2  ! also belongs to the default namespace
my_package_FPM_my_mod ! belongs to namespace `my_package`

3. Namespace priority/cascade

Within a namespace, no duplicate module names are allowed and in general, namespace==package, but not necessarily. I would vote for not prefixing all modules by default, but only resolving potentially colliding ones. In this case, something like:

• Is namespace required in the dependency manifest? Resolve to its modules first;
• Fallback to default / not-defined modules otherwise

Prior Art

PHP has good guidelines

Additional Information

Also related to #814

[perazz]

I'm wondering if choosing _FPM_ is a good choice for the namespace identifier. That string could be part of both a valid module name or even a namespace which could cause confusion. So it may be better to use a reserved character like % or \ instead.