bitset: initial state, play with fold expr

1 files changed, 99 insertions, 0 deletions

diff --git a/bitset.h b/bitset.h
new file mode 100644
index 0000000..638a126
--- /dev/null
+++ b/bitset.h
@@ -0,0 +1,99 @@
+#ifndef UTILS_BITSET_H
+#define UTILS_BITSET_H
+
+#include <cassert>
+#include <type_traits>
+
+// -- BITSET -------------------------------------------------------------------
+
+/// bitset
+///
+/// A simple bitset type, to experiment with with c++17 fold expressions and
+/// type checked template argument packs.
+///
+/// Typically a bitset<> is created from an enum holding the bits of interest.
+///
+/// ```
+/// enum mybits { x, y, z };
+///
+/// bitset<mybits> b;
+///
+/// b.set(x, y)
+/// assert(b.is_set(x));
+/// assert(b.any(x,z));
+/// assert(!b.all(x,z));
+/// ```
+template <typename Bits>
+struct bitset {
+  using bits_t = std::underlying_type_t<Bits>;
+
+  // -- CONSTRUCTOR ------------------------------------------------------------
+
+  template <typename... Bit>
+  constexpr explicit bitset(Bit... bit) {
+    (set(bit), ...);
+  }
+
+  // -- SET/UNSET --------------------------------------------------------------
+
+  template <typename... Bit>
+  void set(Bit... bit) {
+    (op<Bit>([&]() { set(bit); }), ...);
+  }
+
+  void set(Bits v) {
+    m_val |= shifted(v);
+  }
+
+  template <typename... Bit>
+  void unset(Bit... bit) {
+    (op<Bit>([&]() { unset(bit); }), ...);
+  }
+
+  void unset(Bits v) {
+    m_val &= ~shifted(v);
+  }
+
+  void clear() {
+    m_val = 0;
+  }
+
+  // -- QUERY ------------------------------------------------------------------
+
+  constexpr bool is_empty() const {
+    return m_val == 0;
+  }
+
+  constexpr bool is_set(Bits v) const {
+    return m_val & shifted(v);
+  }
+
+  template <typename... Bit>
+  constexpr bool any(Bit... bit) const {
+    return (is_set(bit) || ...);
+  }
+
+  template <typename... Bit>
+  constexpr bool all(Bit... bit) const {
+    return sizeof...(Bit) == 0 ? false : (is_set(bit) && ...);
+  }
+
+  // -- INTERNAL ---------------------------------------------------------------
+
+ private:
+  constexpr static bits_t shifted(Bits bit) {
+    assert(0 <= bit && bit < static_cast<bits_t>(sizeof(bits_t) * 8));
+    return static_cast<bits_t>(1) << bit;
+  }
+
+  template <typename T, typename F>
+  static constexpr auto op(F&& f) -> decltype(f()) {
+    static_assert(std::is_same_v<Bits, T>);
+    return f();
+  }
+
+ private:
+  bits_t m_val = 0;
+};
+
+#endif