Add some skeleton code for GPU support.

src/storage.rs

@@ -20,6 +20,7 @@ impl CpuStorage {
 #[derive(Debug, Clone)]
 pub enum Storage {
     Cpu(CpuStorage),
+    Cuda { gpu_id: usize }, // TODO: Actually add the storage.
 }
 
 trait UnaryOp {
@@ -116,12 +117,14 @@ impl Storage {
     pub fn device(&self) -> Device {
         match self {
             Self::Cpu(_) => Device::Cpu,
+            Self::Cuda { gpu_id } => Device::Cuda { gpu_id: *gpu_id },
         }
     }
 
     pub fn dtype(&self) -> DType {
         match self {
             Self::Cpu(storage) => storage.dtype(),
+            Self::Cuda { .. } => todo!(),
         }
     }
 
@@ -168,6 +171,7 @@ impl Storage {
                     Ok(Storage::Cpu(CpuStorage::F64(data)))
                 }
             },
+            Self::Cuda { .. } => todo!(),
         }
     }
 
@@ -186,6 +190,7 @@ impl Storage {
                     Ok(Storage::Cpu(CpuStorage::F64(data)))
                 }
             },
+            Self::Cuda { .. } => todo!(),
         }
     }
 
@@ -232,6 +237,16 @@ impl Storage {
                     })
                 }
             },
+            (Self::Cuda { .. }, Self::Cuda { .. }) => todo!(),
+            (lhs, rhs) => {
+                // Should not happen because of the same device check above but we're defensive
+                // anyway.
+                Err(Error::DeviceMismatchBinaryOp {
+                    lhs: lhs.device(),
+                    rhs: rhs.device(),
+                    op: B::NAME,
+                })
+            }
         }
     }