Macro project_global 

macro_rules! project_global {
    (mut $global:expr => $($path:tt)+) => { ... };
    ($global:expr => $($path:tt)+) => { ... };
}

Project a field of a global container (crate::SharedGlobal or crate::SharedGlobalMut) as a crate::Shared or crate::SharedMut, in a const context.

project_global!(GLOBAL => path) returns a read-only crate::Shared; project_global!(mut GLOBAL => path) returns a crate::SharedMut (and requires the global to be a crate::SharedGlobalMut). Because the projection is built entirely from function pointers, the result can initialize another static:

struct App {
    name: String,
    port: u16,
}
static APP: SharedGlobalMut<App> = SharedGlobalMut::new_lazy(|| App {
    name: "server".to_string(),
    port: 80,
});
static NAME: SharedMut<String> = project_global!(mut APP => name);
static PORT: Shared<u16> = project_global!(APP => port);

*NAME.write() += "-1";
assert_eq!(APP.read().name, "server-1");
assert_eq!(*PORT.read(), 80);

The global must be referred to by its path (e.g. APP or config::APP): the generated lock functions are non-capturing closures, so a local variable cannot be used here.