Environment specific files

V provides the ability to create files that will only be used in a specific environment. For example, only on Windows, or only on Linux.

If a file has an environment-specific suffix, it will only be compiled for that environment.

.js.v – will be used only by the JS backend. These files can contain JS.* declarations.
.c.v – will be used only by the C backend. These files can contain C.* declarations.
.native.v – will be used only by V's native backend.
_nix.c.v – will be used only on Unix systems (non-Windows).
_${os}.c.v – will be used only on the specific os system. For example, _windows.c.v will be used only when compiling on Windows, or with -os windows.
_default.c.v – will be used only if there is NOT a more specific platform file. For example, if you have both file_linux.c.v and file_default.c.v, and you are compiling for linux, then only file_linux.c.v will be used, and file_default.c.v will be ignored.

Here is a more complete example:

main.v:

module main fn main() { println(message) }

main_default.c.v:

module main const ( message = 'Hello, World!' )

main_linux.c.v:

module main const ( message = 'Hello, Linux!' )

main_windows.c.v:

module main const ( message = 'Hello, Windows!' )

With the example above:

when you compile for Windows, you will get 'Hello, Windows!'
when you compile for Linux, you will get 'Hello, Linux!'
when you compile for any other platform, you will get the non-specific 'Hello, World!' message.

_d_customflag.v – will be used only if you pass -d customflag to V. That corresponds to $if customflag ? {}, but for a whole file, not just a single block. customflag should be a snake_case identifier, it can not contain arbitrary characters (only lower case latin letters + numbers + _).

A combinatorial _d_customflag_linux.c.v postfix will not work. If you do need a custom flag file, that has platform dependent code, use the postfix _d_customflag.v, and then use platform dependent compile time conditional blocks inside it, i.e. $if linux {} etc.

_notd_customflag.v – similar to _d_customflag.v, but will be used only if you do NOT pass -d customflag to V.