Philip Withnall
philip.withnall@collabora.co.uk 2015, 2016
Avoiding symbol conflicts between libraries by namespacing all APIs

# Namespacing

#

        Sumar

          If a library is namespaced correctly, it can define types and methods in
          its API which have the same names as those in another library, and a
          program can use both without conflicts. This is achieved by prefixing all
          types and method names with a namespace unique to the library.

# GObject APIs

Consistent and complete namespacing of symbols (functions and types) and files is important for two key reasons:

Establishing a convention which means developers have to learn fewer symbol names to use the library — they can guess them reliably instead.

Ensuring symbols from two projects do not conflict if included in the same file.

The second point is important — imagine what would happen if every project exported a function called `create_object()`. The headers defining them could not be included in the same file, and even if that were overcome, the programmer would not know which project each function comes from. Namespacing eliminates these problems by using a unique, consistent prefix for every symbol and filename in a project, grouping symbols into their projects and separating them from others.

The conventions below should be used for namespacing all symbols. They are used in all GLib-based projects, so should be familiar to a lot of developers:

Functions should use `lower_case_with_underscores`.

Structures, types and objects should use `CamelCaseWithoutUnderscores`.

Macros and constants should use `UPPER_CASE_WITH_UNDERSCORES`.

All symbols should be prefixed with a short (2–4 characters) version of the namespace. This is shortened purely for ease of typing, but should still be unique.

All methods of a class should also be prefixed with the class name.

Additionally, public headers should be included from a subdirectory, effectively namespacing the header files. For example, instead of `#include <abc.h>`, a project should allow its users to use `#include <namespace/abc.h>`.

Some projects namespace their headers within this subdirectory — for example, `#include <namespace/ns-abc.h>` instead of `#include <namespace/abc.h>`. This is redundant, but harmless.

For example, for a project called ‘Walbottle’, the short namespace ‘Wbl’ would be chosen. If it has a ‘schema’ class and a ‘writer’ class, it would install headers:

$(includedir)/walbottle-$API_MAJOR/walbottle/schema.h

$(includedir)/walbottle-$API_MAJOR/walbottle/writer.h

(The use of $API_MAJOR above is for parallel installability.)

For the schema class, the following symbols would be exported (amongst others), following GObject conventions:

`WblSchema` structure

`WblSchemaClass` structure

`WBL_TYPE_SCHEMA` macro

`WBL_IS_SCHEMA` macro

`wbl_schema_get_type` function

`wbl_schema_new` function

`wbl_schema_load_from_data` function