Rewrite crate to operate on reference values

.github/workflows/build.yml

@@ -0,0 +1,95 @@
+# Based on https://github.com/actions-rs/meta/blob/master/recipes/quickstart.md
+#
+# While our "example" application has the platform-specific code,
+# for simplicity we are compiling and testing everything on the Ubuntu environment only.
+# For multi-OS testing see the `cross.yml` workflow.
+
+on: [push, pull_request]
+
+name: Build
+
+jobs:
+  check:
+    name: Check
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v2
+
+      - name: Install stable toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+
+      - name: Run cargo check
+        uses: actions-rs/cargo@v1
+        with:
+          command: check
+
+  test:
+    name: Test Suite
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v2
+
+      - name: Install stable toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+
+      - name: Run cargo test
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+
+  unstable:
+    name: Test Suite (unstable)
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v2
+
+      - name: Install nightly toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: nightly
+          override: true
+
+      - name: Run cargo test --features unstable
+        uses: actions-rs/cargo@v1
+        with:
+          command: test
+          args: --features unstable
+
+
+  lints:
+    name: Lints
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout sources
+        uses: actions/checkout@v2
+
+      - name: Install stable toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: stable
+          override: true
+          components: rustfmt, clippy
+
+      - name: Run cargo fmt
+        uses: actions-rs/cargo@v1
+        with:
+          command: fmt
+          args: --all -- --check
+
+      - name: Run cargo clippy
+        uses: actions-rs/cargo@v1
+        with:
+          command: clippy

Cargo.toml

@@ -11,11 +11,15 @@ repository = "https://github.com/phil-opp/volatile"
 [dependencies]
 
 [features]
-const_fn = []
+# Enable unstable features; requires Rust nightly; might break on compiler updates
+unstable = []
 
 [package.metadata.release]
 no-dev-version = true
 pre-release-replacements = [
     { file="Changelog.md", search="# Unreleased", replace="# Unreleased\n\n# {{version}} – {{date}}", exactly=1 },
 ]
 pre-release-commit-message = "Release version {{version}}"
+
+[package.metadata.docs.rs]
+features = ["unstable"]

src/access.rs

@@ -0,0 +1,22 @@
+/// Helper trait that is implemented by [`ReadWrite`] and [`ReadOnly`].
+pub trait Readable {}
+
+/// Helper trait that is implemented by [`ReadWrite`] and [`WriteOnly`].
+pub trait Writable {}
+
+/// Zero-sized marker type for allowing both read and write access.
+#[derive(Debug, Copy, Clone)]
+pub struct ReadWrite;
+impl Readable for ReadWrite {}
+impl Writable for ReadWrite {}
+
+/// Zero-sized marker type for allowing only read access.
+#[derive(Debug, Copy, Clone)]
+pub struct ReadOnly;
+
+impl Readable for ReadOnly {}
+
+/// Zero-sized marker type for allowing only write access.
+#[derive(Debug, Copy, Clone)]
+pub struct WriteOnly;
+impl Writable for WriteOnly {}