Merge branch 'vfs' into 'develop-BA-FS26'

implement basic vfs

See merge request teachos/kernel!16

4 files changed, 1102 insertions, 37 deletions

diff --git a/libs/kstd/CMakeLists.txt b/libs/kstd/CMakeLists.txt
index 06543ab..d4f415f 100644
--- a/libs/kstd/CMakeLists.txt
+++ b/libs/kstd/CMakeLists.txt
@@ -46,6 +46,7 @@ if(NOT CMAKE_CROSSCOMPILING)
     add_executable("kstd_tests"
         "tests/src/vector.cpp"
         "tests/src/os_panic.cpp"
+        "tests/src/string.cpp"
     )
 
     target_include_directories("kstd_tests" PRIVATE
diff --git a/libs/kstd/include/kstd/bits/shared_ptr.hpp b/libs/kstd/include/kstd/bits/shared_ptr.hpp
index 6bce83f..8930095 100644
--- a/libs/kstd/include/kstd/bits/shared_ptr.hpp
+++ b/libs/kstd/include/kstd/bits/shared_ptr.hpp
@@ -10,10 +10,200 @@
 
 namespace kstd
 {
+  /**
+   * @brief Control block for shared_ptr and weak_ptr. This control block contains the reference counts for shared
+   * ownership and weak ownership. The shared_count tracks the number of shared_ptr instances that own the managed
+   * object, while the weak_count tracks the number of weak_ptr instances that reference the managed object.
+   * The weak_count is needed to determine when it is safe to delete the shared_control_block itself
+   */
+  struct shared_control_block
+  {
+    std::atomic<std::size_t> shared_count;
+    std::atomic<std::size_t> weak_count;
+
+    explicit shared_control_block(std::size_t shared = 1, std::size_t weak = 0)
+        : shared_count(shared)
+        , weak_count(weak)
+    {}
+  };
+
   template<typename T>
   struct shared_ptr;
 
   /**
+   * @brief weak_ptr is a smart pointer that holds a non-owning weak reference to an object that is managed by
+   * shared_ptr. It must be converted to shared_ptr in to be able to access the referenced object. A weak_ptr is created
+   * as a copy of a shared_ptr, or as a copy of another weak_ptr. A weak_ptr is typically used to break circular
+   * references between shared_ptr to avoid memory leaks. A weak_ptr does not contribute to the reference count of the
+   * object, and it does not manage the lifetime of the object. If the object managed by shared_ptr is destroyed, the
+   * weak_ptr becomes expired and cannot be used to access the object anymore.
+   */
+  template<typename T>
+  struct weak_ptr
+  {
+    template<typename U>
+    friend struct shared_ptr;
+
+    /**
+     * @brief Constructs a null weak_ptr.
+     */
+    weak_ptr() noexcept
+        : pointer(nullptr)
+        , control(nullptr)
+    {}
+
+    template<typename U>
+      requires(std::is_convertible_v<U *, T *>)
+    weak_ptr(shared_ptr<U> const & other)
+        : pointer(other.pointer)
+        , control(other.control)
+    {
+      if (control != nullptr)
+      {
+        ++(control->weak_count);
+      }
+    }
+
+    /**
+     * @brief Copy constructor. Constructs a weak_ptr which shares ownership of the object managed by other.
+     */
+    weak_ptr(weak_ptr const & other)
+        : pointer(other.pointer)
+        , control(other.control)
+    {
+      if (control != nullptr)
+      {
+        ++(control->weak_count);
+      }
+    }
+
+    /**
+     * @brief Move constructor. Constructs a weak_ptr which takes ownership of the object managed by other.
+     */
+    weak_ptr(weak_ptr && other) noexcept
+        : pointer(other.pointer)
+        , control(other.control)
+    {
+      other.pointer = nullptr;
+      other.control = nullptr;
+    }
+
+    /**
+     * @brief Assignment operator. Assigns the weak_ptr to another weak_ptr.
+     */
+    auto operator=(weak_ptr const & other) -> weak_ptr &
+    {
+      if (this != &other)
+      {
+        cleanup();
+        pointer = other.pointer;
+        control = other.control;
+        if (control != nullptr)
+        {
+          ++(control->weak_count);
+        }
+      }
+
+      return *this;
+    }
+
+    /**
+     * @brief Move assignment operator. Move-assigns a weak_ptr from other.
+     */
+    auto operator=(weak_ptr && other) noexcept -> weak_ptr &
+    {
+      if (this != &other)
+      {
+        cleanup();
+        pointer = other.pointer;
+        control = other.control;
+        other.pointer = nullptr;
+        other.control = nullptr;
+      }
+
+      return *this;
+    }
+
+    /**
+     * @brief Destructor. Cleans up resources if necessary.
+     */
+    ~weak_ptr()
+    {
+      cleanup();
+    }
+
+    /**
+     * @brief Returns a shared_ptr that shares ownership of the managed object if the managed object still exists, or an
+     * empty shared_ptr otherwise.
+     */
+    [[nodiscard]] auto lock() const -> shared_ptr<T>
+    {
+      return shared_ptr<T>(*this);
+    }
+
+  private:
+    auto cleanup() -> void
+    {
+      if (control != nullptr)
+      {
+        if (--(control->weak_count) == 0 && control->shared_count == 0)
+        {
+          delete control;
+        }
+      }
+    }
+
+    T * pointer;
+    shared_control_block * control;
+  };
+
+  /**
+   * @brief enable_shared_from_this is a base class that allows an object that is currently managed by a shared_ptr to
+   * create additional shared_ptr instances that share ownership of the same object. This is usefl when you want to
+   * create shared_ptr instances in a member function of the object.
+   *
+   * @tparam T The type of the managed object.
+   */
+  template<typename T>
+  struct enable_shared_from_this
+  {
+    template<typename U>
+    friend struct shared_ptr;
+
+    friend T;
+
+  public:
+    /**
+     * @brief Returns a shared_ptr that shares ownership of *this.
+     */
+    auto shared_from_this() -> shared_ptr<T>
+    {
+      return shared_ptr<T>(weak_this);
+    }
+
+    /**
+     * @brief Returns a shared_ptr that shares ownership of *this.
+     */
+    auto shared_from_this() const -> shared_ptr<T const>
+    {
+      return shared_ptr<T const>(weak_this);
+    }
+
+  private:
+    enable_shared_from_this() = default;
+    enable_shared_from_this(enable_shared_from_this const &) = default;
+    auto operator=(enable_shared_from_this const &) -> enable_shared_from_this & = default;
+    ~enable_shared_from_this() = default;
+
+    void internal_assign_ptr(shared_ptr<T> const & ptr) const
+    {
+      weak_this = ptr;
+    }
+
+    mutable weak_ptr<T> weak_this{};  ///< Weak pointer to the object, used for shared_from_this functionality.
+  };
+
+  /**
    * @brief Shared_pointer is a smart pointer that retains shared ownership of an object through a pointer. Several
    * shared_ptr objects may own the same object. The object is destroyed and its memory deallocated when either of
    * the following happens: the last remaining shared_ptr owning the object is destroyed; the last remaining
@@ -31,12 +221,23 @@ namespace kstd
     template<typename U>
     friend struct shared_ptr;
 
+    template<typename U>
+    friend struct weak_ptr;
+
+    /**
+     * @brief Construct an empty shared_ptr.
+     */
+    shared_ptr() noexcept
+        : pointer(nullptr)
+        , control(nullptr)
+    {}
+
     /**
      * @brief Construct an empty shared_ptr from nullptr.
      */
     shared_ptr(std::nullptr_t) noexcept
         : pointer(nullptr)
-        , ref_count(nullptr)
+        , control(nullptr)
     {}
 
     /**
@@ -44,11 +245,33 @@ namespace kstd
      *
      * @param pointer A pointer to an object to manage (default is nullptr).
      */
-    explicit shared_ptr(T * pointer = nullptr)
+    template<typename U>
+      requires(std::is_convertible_v<U *, T *>)
+    explicit shared_ptr(U * pointer = nullptr)
         : pointer(pointer)
-        , ref_count(pointer != nullptr ? new std::atomic<std::size_t>(1) : nullptr)
+        , control(pointer != nullptr ? new shared_control_block() : nullptr)
+    {
+      assign_enable_shared_from_this(pointer);
+    }
+
+    /**
+     * @brief Constructor a shared_ptr from a weak_ptr. If other is not expired, constructs a shared_ptr which shares
+     * ownership of the object managed by other. Otherwise, constructs an empty shared_ptr.
+     *
+     * @param other The weak_ptr to construct from.
+     */
+    template<typename U>
+      requires(std::is_convertible_v<U *, T *>)
+    explicit shared_ptr(weak_ptr<U> const & other)
+        : pointer(nullptr)
+        , control(nullptr)
     {
-      // Nothing to do.
+      if (other.control != nullptr && other.control->shared_count != 0)
+      {
+        pointer = other.pointer;
+        control = other.control;
+        ++(control->shared_count);
+      }
     }
 
     /**
@@ -58,11 +281,11 @@ namespace kstd
      */
     shared_ptr(shared_ptr const & other)
         : pointer(other.pointer)
-        , ref_count(other.ref_count)
+        , control(other.control)
     {
-      if (ref_count != nullptr)
+      if (control != nullptr)
       {
-        ++(*ref_count);
+        ++(control->shared_count);
       }
     }
 
@@ -76,11 +299,11 @@ namespace kstd
       requires(std::is_convertible_v<U *, T *>)
     shared_ptr(shared_ptr<U> const & other)
         : pointer(other.pointer)
-        , ref_count(other.ref_count)
+        , control(other.control)
     {
-      if (ref_count != nullptr)
+      if (control != nullptr)
       {
-        ++(*ref_count);
+        ++(control->shared_count);
       }
     }
 
@@ -91,10 +314,10 @@ namespace kstd
      */
     shared_ptr(shared_ptr && other) noexcept
         : pointer(other.pointer)
-        , ref_count(other.ref_count)
+        , control(other.control)
     {
       other.pointer = nullptr;
-      other.ref_count = nullptr;
+      other.control = nullptr;
     }
 
     /**
@@ -107,10 +330,10 @@ namespace kstd
       requires(std::is_convertible_v<U *, T *>)
     shared_ptr(shared_ptr<U> && other) noexcept
         : pointer(other.pointer)
-        , ref_count(other.ref_count)
+        , control(other.control)
     {
       other.pointer = nullptr;
-      other.ref_count = nullptr;
+      other.control = nullptr;
     }
 
     /**
@@ -127,11 +350,11 @@ namespace kstd
       {
         cleanup();
         pointer = other.pointer;
-        ref_count = other.ref_count;
+        control = other.control;
 
-        if (ref_count != nullptr)
+        if (control != nullptr)
         {
-          ++(*ref_count);
+          ++(control->shared_count);
         }
       }
 
@@ -151,11 +374,11 @@ namespace kstd
     {
       cleanup();
       pointer = other.pointer;
-      ref_count = other.ref_count;
+      control = other.control;
 
-      if (ref_count != nullptr)
+      if (control != nullptr)
       {
-        ++(*ref_count);
+        ++(control->shared_count);
       }
 
       return *this;
@@ -174,9 +397,9 @@ namespace kstd
       {
         cleanup();
         pointer = other.pointer;
-        ref_count = other.ref_count;
+        control = other.control;
         other.pointer = nullptr;
-        other.ref_count = nullptr;
+        other.control = nullptr;
       }
 
       return *this;
@@ -195,9 +418,9 @@ namespace kstd
     {
       cleanup();
       pointer = other.pointer;
-      ref_count = other.ref_count;
+      control = other.control;
       other.pointer = nullptr;
-      other.ref_count = nullptr;
+      other.control = nullptr;
 
       return *this;
     }
@@ -209,7 +432,7 @@ namespace kstd
     {
       cleanup();
       pointer = nullptr;
-      ref_count = nullptr;
+      control = nullptr;
       return *this;
     }
 
@@ -230,7 +453,8 @@ namespace kstd
     {
       cleanup();
       pointer = ptr;
-      ref_count = ptr != nullptr ? new std::atomic<std::size_t>(1) : nullptr;
+      control = ptr != nullptr ? new shared_control_block() : nullptr;
+      assign_enable_shared_from_this(ptr);
     }
 
     /**
@@ -242,7 +466,7 @@ namespace kstd
     void swap(shared_ptr & other)
     {
       std::swap(pointer, other.pointer);
-      std::swap(ref_count, other.ref_count);
+      std::swap(control, other.control);
     }
 
     /**
@@ -288,9 +512,9 @@ namespace kstd
      */
     [[nodiscard]] auto use_count() const -> std::size_t
     {
-      if (ref_count != nullptr)
+      if (control != nullptr)
       {
-        return *ref_count;
+        return control->shared_count;
       }
 
       return 0;
@@ -322,26 +546,49 @@ namespace kstd
       return ptr.pointer == nullptr;
     }
 
+  private:
     /**
-     * @brief Defaulted three-way comparator operator.
+     * @brief If the candidate type inherits from enable_shared_from_this, assigns the internal weak pointer to this
+     * shared_ptr. This weak_ptr is used to implement shared_from_this functionality for the candidate type. If the
+     * candidate type does not inherit from enable_shared_from_this, this function does nothing.
+     *
+     * @tparam U The candidate type to check for enable_shared_from_this inheritance.
+     * @param candidate The candidate object to assign the internal weak pointer for.
      */
-    [[nodiscard]] auto operator<=>(shared_ptr const & other) const = default;
+    template<typename U>
+    auto assign_enable_shared_from_this(U * candidate) -> void
+    {
+      if constexpr (requires(U * p, shared_ptr<T> const & sp) { p->internal_assign_ptr(sp); })
+      {
+        if (candidate != nullptr)
+        {
+          candidate->internal_assign_ptr(*this);
+        }
+      }
+    }
 
-  private:
     /**
      * @brief Releases ownership and deletes the object if this was the last reference to the owned managed object.
      */
     auto cleanup() -> void
     {
-      if (ref_count != nullptr && --(*ref_count) == 0)
+      if (control != nullptr)
       {
-        delete pointer;
-        delete ref_count;
+        if (--(control->shared_count) == 0)
+        {
+          delete pointer;
+          pointer = nullptr;
+
+          if (control->weak_count == 0)
+          {
+            delete control;
+          }
+        }
       }
     }
 
-    T * pointer;                           ///< The managed object.
-    std::atomic<std::size_t> * ref_count;  ///< Reference count.
+    T * pointer;                     ///< The managed object.
+    shared_control_block * control;  ///< Shared control block.
   };
 
   /**
@@ -372,6 +619,30 @@ namespace kstd
   {
     return shared_ptr<T>(new T(std::forward<Args>(args)...));
   }
+
+  /**
+   * @brief Equality operator for shared_ptr. Two shared_ptr instances are equal if they point to the same object
+   * @tparam T, U Types of the managed objects of the shared_ptr instances being compared.
+   * @param lhs, rhs The shared_ptr instances to compare.
+   * @return true if lhs and rhs point to the same object, false otherwise.
+   */
+  template<typename T, typename U>
+  [[nodiscard]] auto inline operator==(shared_ptr<T> const & lhs, shared_ptr<U> const & rhs) -> bool
+  {
+    return lhs.get() == rhs.get();
+  }
+
+  /**
+   * @brief Three-way comparison operator for shared_ptr. Compares the stored pointers of lhs and rhs using operator<=>.
+   * @tparam T, U Types of the managed objects of the shared_ptr instances being compared.
+   * @param lhs, rhs The shared_ptr instances to compare.
+   * @return The result of comparing the stored pointers of lhs and rhs using operator<=>
+   */
+  template<typename T, typename U>
+  [[nodiscard]] auto inline operator<=>(shared_ptr<T> const & lhs, shared_ptr<U> const & rhs)
+  {
+    return lhs.get() <=> rhs.get();
+  }
 }  // namespace kstd
 
 #endif
\ No newline at end of file
diff --git a/libs/kstd/include/kstd/string b/libs/kstd/include/kstd/string
new file mode 100644
index 0000000..075422e
--- /dev/null
+++ b/libs/kstd/include/kstd/string
@@ -0,0 +1,348 @@
+#ifndef KSTD_STRING_HPP
+#define KSTD_STRING_HPP
+
+#include <kstd/cstring>
+#include <kstd/os/error.hpp>
+#include <kstd/vector>
+
+#include <algorithm>
+#include <concepts>
+#include <cstddef>
+#include <string_view>
+
+namespace kstd
+{
+  /**
+   * @brief A simple string implementation that owns its data and provides basic operations.
+   */
+  struct string
+  {
+    //! The type of the characters contained in this string.
+    using value_type = char;
+    //! The type of the underlying storage used by this string.
+    using storage_type = kstd::vector<value_type>;
+    //! The type of all sizes used in and with this string.
+    using size_type = std::size_t;
+    //! The type of the difference between two iterators.
+    using difference_type = std::ptrdiff_t;
+    //! The type of references to single values in this string.
+    using reference = value_type &;
+    //! The type of references to constant single values in this string.
+    using const_reference = value_type const &;
+    //! The type of pointers to single values in this string.
+    using pointer = value_type *;
+    //! The type of pointers to constant single values in this string.
+    using const_pointer = value_type const *;
+    //! The type of iterators into this string.
+    using iterator = pointer;
+    //! The type of constant iterators into this string.
+    using const_iterator = const_pointer;
+
+    /**
+     * @brief Constructs an empty null-terminated string.
+     */
+    string()
+        : m_storage{value_type{'\0'}}
+    {}
+
+    /**
+     * @brief Constructs a string from a string view by copying the characters into owned storage.
+     * @param view The string view to copy the characters from.
+     */
+    string(std::string_view view)
+        : string()
+    {
+      append(view);
+    }
+
+    /**
+     * @brief Constructs a string from a null-terminated C-style string by copying the characters into owned storage.
+     * @param c_str The null-terminated C-style string to copy.
+     */
+    string(char const * c_str)
+        : string()
+    {
+      if (c_str != nullptr)
+      {
+        append(std::string_view{c_str});
+      }
+    }
+
+    /**
+     * @brief Constructs a string containing a single character.
+     * @param c The character to copy.
+     */
+    string(value_type c)
+        : string()
+    {
+      push_back(c);
+    }
+
+    /**
+     * @brief Constructs a string by copying another string.
+     * @param other The string to copy.
+     */
+    constexpr string(string const & other)
+        : m_storage{other.m_storage}
+    {}
+
+    /**
+     * @brief Destructs the string.
+     */
+    constexpr ~string() = default;
+
+    /**
+     * @brief Assigns the value of another string to this string.
+     * @param other The string to assign from.
+     * @return A reference to this string.
+     */
+    constexpr auto operator=(string const & other) -> string & = default;
+
+    /**
+     * @brief Returns the number of characters in this string, not including the null terminator.
+     */
+    [[nodiscard]] constexpr auto size() const noexcept -> size_type
+    {
+      return m_storage.empty() ? 0 : m_storage.size() - 1;
+    }
+
+    /**
+     * @brief Checks if this string is empty, not including the null terminator.
+     */
+    [[nodiscard]] constexpr auto empty() const noexcept -> bool
+    {
+      return size() == 0;
+    }
+
+    /**
+     * @brief Clears the content of the string, resulting in an empty string.
+     * The string remains null-terminated after this operation.
+     */
+    constexpr auto clear() -> void
+    {
+      m_storage.clear();
+      m_storage.push_back(value_type{'\0'});
+    }
+
+    //! Get a pointer to the underlying storage of the string
+    [[nodiscard]] constexpr auto data() noexcept -> pointer
+    {
+      return m_storage.data();
+    }
+
+    //! Get a const pointer to the underlying storage of the string
+    [[nodiscard]] constexpr auto data() const noexcept -> const_pointer
+    {
+      return m_storage.data();
+    }
+
+    //! Get a const pointer to the underlying storage of the string
+    [[nodiscard]] constexpr auto c_str() const noexcept -> const_pointer
+    {
+      return data();
+    }
+
+    //! Get an iterator to the beginning of the string
+    [[nodiscard]] constexpr auto begin() noexcept -> iterator
+    {
+      return data();
+    }
+
+    //! Get an const iterator to the beginning of the string
+    [[nodiscard]] constexpr auto begin() const noexcept -> const_iterator
+    {
+      return data();
+    }
+
+    //! Get an const iterator to the beginning of the string
+    [[nodiscard]] constexpr auto cbegin() const noexcept -> const_iterator
+    {
+      return begin();
+    }
+
+    //! Get an iterator to the end of the string
+    [[nodiscard]] constexpr auto end() noexcept -> iterator
+    {
+      return data() + size();
+    }
+
+    //! Get an const iterator to the end of the string
+    [[nodiscard]] constexpr auto end() const noexcept -> const_iterator
+    {
+      return data() + size();
+    }
+
+    //! Get an const iterator to the end of the string
+    [[nodiscard]] constexpr auto cend() const noexcept -> const_iterator
+    {
+      return end();
+    }
+
+    //! Get a reference to the first character of the string
+    [[nodiscard]] constexpr auto front() -> reference
+    {
+      return m_storage.front();
+    }
+
+    //! Get a const reference to the first character of the string
+    [[nodiscard]] constexpr auto front() const -> const_reference
+    {
+      return m_storage.front();
+    }
+
+    //! Get a reference to the last character of the string
+    [[nodiscard]] constexpr auto back() -> reference
+    {
+      return m_storage[size() - 1];
+    }
+
+    //! Get a const reference to the last character of the string
+    [[nodiscard]] constexpr auto back() const -> const_reference
+    {
+      return m_storage[size() - 1];
+    }
+
+    /**
+     * @brief Appends a character to the end of the string.
+     * @param ch The character to append.
+     */
+    constexpr auto push_back(value_type ch) -> void
+    {
+      m_storage.back() = ch;
+      m_storage.push_back(value_type{'\0'});
+    }
+
+    /**
+     * @brief Appends a string view to the end of the string by copying the characters into owned storage.
+     * @param view The string view to append.
+     * @return A reference to this string.
+     */
+    constexpr auto append(std::string_view view) -> string &
+    {
+      if (!view.empty())
+      {
+        std::ranges::for_each(view, [this](auto const ch) { push_back(ch); });
+      }
+
+      return *this;
+    }
+
+    /**
+     * @brief Appends another string to the end of this string by copying the characters into owned storage.
+     * @param other The string to append.
+     * @return A reference to this string.
+     */
+    constexpr auto append(string const & other) -> string &
+    {
+      return append(other.view());
+    }
+
+    /**
+     * @brief Appends another string to the end of this string by copying the characters into owned storage.
+     * @param other The string to append.
+     * @return A reference to this string.
+     */
+    constexpr auto operator+=(string const & other) -> string &
+    {
+      return append(other);
+    }
+
+    /**
+     * @brief Appends a character to the end of the string.
+     * @param ch The character to append.
+     * @return A reference to this string.
+     */
+    constexpr auto operator+=(value_type ch) -> string &
+    {
+      push_back(ch);
+      return *this;
+    }
+
+    /**
+     * @brief Returns a string view of this string, which is a non-owning view into the characters of this string.
+     */
+    [[nodiscard]] constexpr auto view() const noexcept -> std::string_view
+    {
+      return std::string_view{data(), size()};
+    }
+
+  private:
+    //! The underlying storage of the string, which owns the characters and ensures null-termination.
+    storage_type m_storage{};
+  };
+
+  /**
+   * @brief Concatenates a strings and a character and returns the result as a new string.
+   * @param lhs The string to concatenate.
+   * @param rhs The string to concatenate.
+   * @return A new string that is the result of concatenating @p lhs and @p rhs.
+   */
+  [[nodiscard]] constexpr auto inline operator+(string const & lhs, string const & rhs) -> string
+  {
+    string result{lhs};
+    result += rhs;
+    return result;
+  }
+
+  /**
+   * @brief Converts an unsigned integer to a string by converting each digit to the corresponding character and
+   * concatenating them.
+   * @tparam N The type of the unsigned integer to convert.
+   * @param value The unsigned integer to convert.
+   * @return A string representation of the given unsigned integer.
+   */
+  template<typename N>
+    requires std::unsigned_integral<N>
+  [[nodiscard]] constexpr auto inline to_string(N value) -> string
+  {
+    if (value == 0)
+    {
+      return "0";
+    }
+
+    string result;
+
+    while (value > 0)
+    {
+      char const digit = '0' + (value % 10);
+      result.push_back(digit);
+      value /= 10;
+    }
+
+    std::reverse(result.begin(), result.end());
+    return result;
+  }
+
+  [[nodiscard]] constexpr auto inline operator==(string const & lhs, string const & rhs) -> bool
+  {
+    return lhs.view() == rhs.view();
+  }
+
+  [[nodiscard]] constexpr auto inline operator!=(string const & lhs, string const & rhs) -> bool
+  {
+    return !(lhs == rhs);
+  }
+
+  [[nodiscard]] constexpr auto inline operator==(string const & lhs, std::string_view rhs) -> bool
+  {
+    return lhs.view() == rhs;
+  }
+
+  [[nodiscard]] constexpr auto inline operator!=(string const & lhs, std::string_view rhs) -> bool
+  {
+    return !(lhs == rhs);
+  }
+
+  [[nodiscard]] constexpr auto inline operator==(std::string_view lhs, string const & rhs) -> bool
+  {
+    return lhs == rhs.view();
+  }
+
+  [[nodiscard]] constexpr auto inline operator!=(std::string_view lhs, string const & rhs) -> bool
+  {
+    return !(lhs == rhs);
+  }
+
+}  // namespace kstd
+
+#endif
\ No newline at end of file
diff --git a/libs/kstd/tests/src/string.cpp b/libs/kstd/tests/src/string.cpp
new file mode 100644
index 0000000..43e9a6b
--- /dev/null
+++ b/libs/kstd/tests/src/string.cpp
@@ -0,0 +1,445 @@
+#include <kstd/string>
+
+#include <catch2/catch_test_macros.hpp>
+
+#include <algorithm>
+#include <ranges>
+#include <string_view>
+
+SCENARIO("String initialization and construction", "[string]")
+{
+  GIVEN("Nothing")
+  {
+    WHEN("constructing an empty string")
+    {
+      auto str = kstd::string{};
+
+      THEN("the size is zero and therefore the string is empty")
+      {
+        REQUIRE(str.empty());
+        REQUIRE(str.size() == 0);
+      }
+
+      THEN("the string is empty")
+      {
+        REQUIRE(str.view() == std::string_view{});
+      }
+    }
+  }
+
+  GIVEN("A string view")
+  {
+    auto view = std::string_view{"Blub Blub"};
+
+    WHEN("constructing a string from string_view")
+    {
+      auto str = kstd::string{view};
+
+      THEN("the string is not empty and has the same size as the view")
+      {
+        REQUIRE(!str.empty());
+        REQUIRE(str.size() == view.size());
+      }
+
+      THEN("the string contains the same characters as the view")
+      {
+        REQUIRE(str.view() == view);
+      }
+    }
+  }
+
+  GIVEN("A C-style string")
+  {
+    auto c_str = "Blub Blub";
+
+    WHEN("constructing a string from the C-style string")
+    {
+      auto str = kstd::string{c_str};
+
+      THEN("the string is not empty and has the same size as the C-style string")
+      {
+        REQUIRE(!str.empty());
+        REQUIRE(str.size() == strlen(c_str));
+      }
+
+      THEN("the string contains the same characters as the C-style string")
+      {
+        REQUIRE(str.view() == c_str);
+      }
+    }
+  }
+
+  GIVEN("A character")
+  {
+    auto ch = 'x';
+
+    WHEN("constructing a string from the character")
+    {
+      auto str = kstd::string{ch};
+
+      THEN("the string is not empty and has size 1")
+      {
+        REQUIRE(!str.empty());
+        REQUIRE(str.size() == 1);
+      }
+
+      THEN("the string contains the same character as the given character")
+      {
+        REQUIRE(str.view() == std::string_view{&ch, 1});
+      }
+    }
+  }
+
+  GIVEN("Another string")
+  {
+    auto other = kstd::string{"Blub Blub"};
+
+    WHEN("copy constructing a new string")
+    {
+      auto str = kstd::string{other};
+
+      THEN("the new string contains the same characters as the original")
+      {
+        REQUIRE(str.view() == other.view());
+      }
+    }
+
+    auto str = kstd::string{"Blub"};
+
+    WHEN("copy assigning another string")
+    {
+      auto other = kstd::string{"Blub Blub"};
+      str = other;
+
+      THEN("the string contains the same characters as the assigned string")
+      {
+        REQUIRE(str.view() == other.view());
+      }
+    }
+  }
+
+  GIVEN("A string")
+  {
+    auto str = kstd::string{"Hello"};
+
+    WHEN("copy assigning a string view")
+    {
+      auto view = std::string_view{"Hello, world!"};
+      str = view;
+
+      THEN("the string contains the same characters as the assigned view")
+      {
+        REQUIRE(str.view() == view);
+      }
+    }
+  }
+
+  GIVEN("A string")
+  {
+    auto str = kstd::string{"Hello"};
+
+    WHEN("copy assigning a C-style string")
+    {
+      auto c_str = "Hello, world!";
+      str = c_str;
+
+      THEN("the string contains the same characters as the assigned C-style string")
+      {
+        REQUIRE(str.view() == c_str);
+      }
+    }
+  }
+}
+
+SCENARIO("String concatenation", "[string]")
+{
+  GIVEN("Two strings")
+  {
+    auto str1 = kstd::string{"Blub"};
+    auto str2 = kstd::string{" Blub"};
+
+    WHEN("appending the second string to the first string")
+    {
+      str1.append(str2);
+
+      THEN("the first string contains the characters of both strings concatenated")
+      {
+        REQUIRE(str1.view() == "Blub Blub");
+      }
+
+      THEN("the size of the first string is the sum of the sizes of both strings")
+      {
+        REQUIRE(str1.size() == str2.size() + 4);
+      }
+    }
+
+    WHEN("using operator+= to append the second string to the first string")
+    {
+      str1 += str2;
+
+      THEN("the first string contains the characters of both strings concatenated")
+      {
+        REQUIRE(str1.view() == "Blub Blub");
+      }
+
+      THEN("the size of the first string is the sum of the sizes of both strings")
+      {
+        REQUIRE(str1.size() == str2.size() + 4);
+      }
+    }
+
+    WHEN("using operator+ to concatenate the two strings into a new string")
+    {
+      auto str3 = str1 + str2;
+
+      THEN("the new string contains the characters of both strings concatenated")
+      {
+        REQUIRE(str3.view() == "Blub Blub");
+      }
+
+      THEN("the size of the new string is the sum of the sizes of both strings")
+      {
+        REQUIRE(str3.size() == str1.size() + str2.size());
+      }
+    }
+  }
+
+  GIVEN("A string and a string view")
+  {
+    auto str = kstd::string{"Blub"};
+    auto view = std::string_view{" Blub"};
+
+    WHEN("appending the string view to the string")
+    {
+      str.append(view);
+
+      THEN("the string contains the characters of both the original string and the appended view concatenated")
+      {
+        REQUIRE(str.view() == "Blub Blub");
+      }
+
+      THEN("the size of the string is the sum of the sizes of the original string and the appended view")
+      {
+        REQUIRE(str.size() == view.size() + 4);
+      }
+    }
+  }
+
+  GIVEN("A string and a character")
+  {
+    auto str = kstd::string{"Blub"};
+    auto ch = '!';