add sum types

1 files changed, 30 insertions, 0 deletions

diff --git a/common/external/nillable.h b/common/external/nillable.h
new file mode 100644
index 0000000..40cf01c
--- /dev/null
+++ b/common/external/nillable.h
@@ -0,0 +1,30 @@
+inline constexpr struct nil_t {} nil;
+
+// Requirements: T is default-constructible and trivially-destructible
+template<typename T>
+struct nillable {
+    bool has_value = false;
+    T value;
+
+    nillable() = default;
+
+    nillable(nil_t) : nillable() {}
+    nillable(const T& v) : has_value(true), value(v) {}
+
+    nillable& operator=(nil_t) {
+        has_value = false;
+        return *this;
+    }
+    nillable& operator=(const T& v) {
+        value = v;
+        has_value = true;
+        return *this;
+    }
+
+    const T* operator->() const { return &value; }
+    T* operator->() { return &value; }
+
+    explicit operator bool() const { return has_value; }
+};
+
+template<typename T> nillable(T)->nillable<T>;