Introduce Cosmopolitan Templates Library (CTL)

ctl/optional.h

@@ -0,0 +1,125 @@
+// -*-mode:c++;indent-tabs-mode:nil;c-basic-offset:4;tab-width:8;coding:utf-8-*-
+// vi: set et ft=c++ ts=4 sts=4 sw=4 fenc=utf-8 :vi
+#ifndef COSMOPOLITAN_CTL_OPTIONAL_H_
+#define COSMOPOLITAN_CTL_OPTIONAL_H_
+#include <__utility/forward.h>
+#include <__utility/move.h>
+#include <__utility/swap.h>
+
+template<typename T>
+class Optional
+{
+  public:
+    using value_type = T;
+
+    ~Optional() = default;
+
+    Optional() noexcept : present_(false)
+    {
+    }
+
+    Optional(const T& value) : present_(true), value_(value)
+    {
+    }
+
+    Optional(T&& value) : present_(true), value_(std::move(value))
+    {
+    }
+
+    Optional(const Optional& other) : present_(other.present_)
+    {
+        if (present_)
+            new (&value_) T(other.value_);
+    }
+
+    Optional(Optional&& other) noexcept : present_(other.present_)
+    {
+        if (present_)
+            value_ = std::move(other.value_);
+    }
+
+    Optional& operator=(const Optional& other)
+    {
+        if (this != &other) {
+            present_ = other.present_;
+            if (present_)
+                value_ = other.value_;
+        }
+        return *this;
+    }
+
+    Optional& operator=(Optional&& other) noexcept
+    {
+        if (this != &other) {
+            present_ = other.present_;
+            if (present_)
+                value_ = std::move(other.value_);
+        }
+        return *this;
+    }
+
+    T& value() &
+    {
+        if (!present_)
+            __builtin_trap();
+        return value_;
+    }
+
+    const T& value() const&
+    {
+        if (!present_)
+            __builtin_trap();
+        return value_;
+    }
+
+    T&& value() &&
+    {
+        if (!present_)
+            __builtin_trap();
+        return std::move(value_);
+    }
+
+    explicit operator bool() const noexcept
+    {
+        return present_;
+    }
+
+    bool has_value() const noexcept
+    {
+        return present_;
+    }
+
+    void reset() noexcept
+    {
+        if (present_) {
+            value_.~T();
+            present_ = false;
+        }
+    }
+
+    template<typename... Args>
+    void emplace(Args&&... args)
+    {
+        present_ = true;
+        value_ = T(std::forward<Args>(args)...);
+    }
+
+    void swap(Optional& other) noexcept
+    {
+        if (present_ && other.present_) {
+            std::swap(value_, other.value_);
+        } else if (present_) {
+            other.emplace(std::move(value_));
+            reset();
+        } else if (other.present_) {
+            emplace(std::move(other.value_));
+            other.reset();
+        }
+    }
+
+  private:
+    bool present_;
+    T value_;
+};
+
+#endif // COSMOPOLITAN_CTL_OPTIONAL_H_