implement allocators as zsts

agb/examples/allocation.rs

@@ -9,9 +9,9 @@ use alloc::boxed::Box;
 #[agb::entry]
 fn main(_gba: agb::Gba) -> ! {
     loop {
-        let a = Box::new_in(1, agb::EWRAM_ALLOC);
+        let a = Box::new_in(1, agb::ExternalAllocator);
         let b = Box::new(1);
-        let c = Box::new_in(3, agb::IWRAM_ALLOC);
+        let c = Box::new_in(3, agb::InternalAllocator);
         agb::println!("ewram allocation made to {:?}", &*a as *const _);
         agb::println!("global allocation made to {:?}", &*b as *const _);
         agb::println!("iwram allocation made to {:?}", &*c as *const _);

agb/src/agb_alloc/mod.rs

@@ -1,4 +1,4 @@
-use core::alloc::Layout;
+use core::alloc::{Allocator, Layout};
 use core::ops::{Deref, DerefMut};
 use core::ptr::NonNull;
 
@@ -43,6 +43,20 @@ static GLOBAL_ALLOC: BlockAllocator = unsafe {
     })
 };
 
+macro_rules! impl_zst_allocator {
+    ($name_of_struct: ty, $name_of_static: ident) => {
+        unsafe impl Allocator for $name_of_struct {
+            fn allocate(&self, layout: Layout) -> Result<NonNull<[u8]>, core::alloc::AllocError> {
+                $name_of_static.allocate(layout)
+            }
+
+            unsafe fn deallocate(&self, ptr: NonNull<u8>, layout: Layout) {
+                $name_of_static.deallocate(ptr, layout)
+            }
+        }
+    };
+}
+
 /// This is the allocator for the External Working Ram. This is currently
 /// equivalent to the Global Allocator (where things are allocated if no allocator is provided). This implements the allocator trait, so
 /// is meant to be used in specifying where certain structures should be
@@ -64,7 +78,9 @@ static GLOBAL_ALLOC: BlockAllocator = unsafe {
 /// );
 /// # }
 /// ```
-pub static EWRAM_ALLOC: &BlockAllocator = &GLOBAL_ALLOC;
+pub struct ExternalAllocator;
+
+impl_zst_allocator!(ExternalAllocator, GLOBAL_ALLOC);
 
 /// This is the allocator for the Internal Working Ram. This implements the
 /// allocator trait, so is meant to be used in specifying where certain
@@ -86,7 +102,10 @@ pub static EWRAM_ALLOC: &BlockAllocator = &GLOBAL_ALLOC;
 /// );
 /// # }
 /// ```
-pub static IWRAM_ALLOC: &BlockAllocator = &__IWRAM_ALLOC;
+pub struct InternalAllocator;
+
+impl_zst_allocator!(InternalAllocator, __IWRAM_ALLOC);
+
 static __IWRAM_ALLOC: BlockAllocator = unsafe {
     BlockAllocator::new(StartEnd {
         start: iwram_data_end,
@@ -227,7 +246,7 @@ mod test {
 
     #[test_case]
     fn allocate_to_iwram_works(_gba: &mut crate::Gba) {
-        let a = Box::new_in(1, IWRAM_ALLOC);
+        let a = Box::new_in(1, InternalAllocator);
         let p = &*a as *const i32;
         let addr = p as usize;
         assert!(

agb/src/lib.rs

@@ -190,7 +190,7 @@ pub mod syscall;
 /// Interactions with the internal timers
 pub mod timer;
 
-pub use {agb_alloc::EWRAM_ALLOC, agb_alloc::IWRAM_ALLOC};
+pub use {agb_alloc::ExternalAllocator, agb_alloc::InternalAllocator};
 
 #[cfg(not(any(test, feature = "testing")))]
 #[panic_handler]
@@ -206,8 +206,6 @@ fn panic_implementation(info: &core::panic::PanicInfo) -> ! {
     loop {}
 }
 
-static mut GBASINGLE: single::Singleton<Gba> = single::Singleton::new(unsafe { Gba::single_new() });
-
 /// The Gba struct is used to control access to the Game Boy Advance's hardware in a way which makes it the
 /// borrow checker's responsibility to ensure no clashes of global resources.
 ///
@@ -245,7 +243,7 @@ impl Gba {
     #[doc(hidden)]
     #[must_use]
     pub unsafe fn new_in_entry() -> Self {
-        GBASINGLE.take()
+        Self::single_new()
     }
 
     const unsafe fn single_new() -> Self {