Optionally implement ConstDefault trait on types

Signed-off-by: Nathaniel McCallum <[email protected]>

Author: npmccallum

.github/workflows/test.yml

@@ -2,7 +2,7 @@ on: [pull_request]
 name: test
 jobs:
   test:
-    name: ${{ matrix.toolchain }} (${{ matrix.profile.name }})
+    name: ${{ matrix.toolchain }} ${{ matrix.profile.name }} ${{ matrix.features }}
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
@@ -13,7 +13,7 @@ jobs:
       - uses: actions-rs/cargo@v1
         with:
           command: test
-          args: ${{ matrix.profile.flag }}
+          args: ${{ matrix.profile.flag }} --features=${{ matrix.features }}
     strategy:
       fail-fast: false
       matrix:
@@ -22,6 +22,9 @@ jobs:
           - beta
           - stable
           - 1.41.0
+        features:
+          -
+          - const-default
         profile:
           - name: debug
           - name: release

Cargo.toml

@@ -19,3 +19,6 @@ github = { repository = "enarx/primordial", workflow = "test" }
 maintenance = { status = "actively-developed" }
 is-it-maintained-issue-resolution = { repository = "enarx/primordial" }
 is-it-maintained-open-issues = { repository = "enarx/primordial" }
+
+[dependencies]
+const-default = { version = "0.1", optional = true }

src/address.rs

@@ -22,7 +22,12 @@ use core::ops::*;
 #[repr(transparent)]
 pub struct Address<T, U>(T, PhantomData<U>);
 
-impl<T: Zero, U: Copy> Address<T, U> {
+#[cfg(feature = "const-default")]
+impl<T: Zero, U> const_default::ConstDefault for Address<T, U> {
+    const DEFAULT: Self = Self::NULL;
+}
+
+impl<T: Zero, U> Address<T, U> {
     /// The NULL address
     pub const NULL: Address<T, U> = Address(T::ZERO, PhantomData);
 }

src/offset.rs

@@ -18,6 +18,11 @@ use core::ops::*;
 #[repr(transparent)]
 pub struct Offset<T, U>(T, PhantomData<U>);
 
+#[cfg(feature = "const-default")]
+impl<T: Zero, U> const_default::ConstDefault for Offset<T, U> {
+    const DEFAULT: Self = Self(T::ZERO, PhantomData);
+}
+
 impl<T, U> Offset<T, U> {
     /// Create an offset value from the number of items
     #[inline]

src/page.rs

@@ -9,6 +9,11 @@ use core::mem::{align_of, align_of_val, size_of, size_of_val};
 #[repr(C, align(4096))]
 pub struct Page([[u64; 32]; 16]);
 
+#[cfg(feature = "const-default")]
+impl const_default::ConstDefault for Page {
+    const DEFAULT: Self = Self([[0; 32]; 16]);
+}
+
 impl Default for Page {
     fn default() -> Self {
         Self([[0; 32]; 16])

src/register.rs

@@ -271,6 +271,11 @@ implptr! {
 #[repr(transparent)]
 pub struct Register<T>(T);
 
+#[cfg(feature = "const-default")]
+impl<T: super::Zero> const_default::ConstDefault for Register<T> {
+    const DEFAULT: Self = Self(T::ZERO);
+}
+
 impl<T> Register<T> {
     /// Converts a register value to a slice
     ///