diff --git a/vector/src/vector.hpp b/vector/src/vector.hpp
index c4d42d0..932914d 100644
--- a/vector/src/vector.hpp
+++ b/vector/src/vector.hpp
@@ -70,7 +70,8 @@ class vector {
     // return the distance between two iterators,
     // if these two iterators point to different vectors, throw invaild_iterator.
     int operator-(const iterator &rhs) const {
-      if (domain != rhs.domain) throw invalid_iterator();
+      if (domain != rhs.domain) [[unlikely]]
+        throw invalid_iterator();
       return raw_pointer - rhs.raw_pointer;
     }
     iterator &operator+=(const int &n) {
@@ -143,7 +144,7 @@ class vector {
    private:
     const vector<T> *domain;
     const T *raw_pointer;
-    const_iterator(const vector<T> *domain, const T *raw_pointer) : domain(domain), raw_pointer(raw_pointer) {}
+    inline const_iterator(const vector<T> *domain, const T *raw_pointer) : domain(domain), raw_pointer(raw_pointer) {}
 
    public:
     /**
@@ -163,7 +164,8 @@ class vector {
     // return the distance between two iterators,
     // if these two iterators point to different vectors, throw invaild_iterator.
     int operator-(const const_iterator &rhs) const {
-      if (domain != rhs.domain) throw invalid_iterator();
+      if (domain != rhs.domain) [[unlikely]]
+        throw invalid_iterator();
       return raw_pointer - rhs.raw_pointer;
     }
     const_iterator &operator+=(const int &n) {
@@ -299,11 +301,13 @@ class vector {
    * throw index_out_of_bound if pos is not in [0, size)
    */
   T &at(const size_t &pos) {
-    if (pos < 0 || pos >= current_length) throw index_out_of_bound();
+    if (pos < 0 || pos >= current_length) [[unlikely]]
+      throw index_out_of_bound();
     return raw_beg[pos];
   }
   const T &at(const size_t &pos) const {
-    if (pos < 0 || pos >= current_length) throw index_out_of_bound();
+    if (pos < 0 || pos >= current_length) [[unlikely]]
+      throw index_out_of_bound();
     return raw_beg[pos];
   }
   /**
@@ -313,11 +317,13 @@ class vector {
    *   In STL this operator does not check the boundary but I want you to do.
    */
   T &operator[](const size_t &pos) {
-    if (pos < 0 || pos >= current_length) throw index_out_of_bound();
+    if (pos < 0 || pos >= current_length) [[unlikely]]
+      throw index_out_of_bound();
     return raw_beg[pos];
   }
   const T &operator[](const size_t &pos) const {
-    if (pos < 0 || pos >= current_length) throw index_out_of_bound();
+    if (pos < 0 || pos >= current_length) [[unlikely]]
+      throw index_out_of_bound();
     return raw_beg[pos];
   }
   /**
@@ -325,7 +331,8 @@ class vector {
    * throw container_is_empty if size == 0
    */
   const T &front() const {
-    if (current_length == 0) throw container_is_empty();
+    if (current_length == 0) [[unlikely]]
+      throw container_is_empty();
     return raw_beg[0];
   }
   /**
@@ -333,7 +340,8 @@ class vector {
    * throw container_is_empty if size == 0
    */
   const T &back() const {
-    if (current_length == 0) throw container_is_empty();
+    if (current_length == 0) [[unlikely]]
+      throw container_is_empty();
     return raw_end[-1];
   }
   /**
@@ -485,7 +493,7 @@ class vector {
    * adds an element to the end.
    */
   void push_back(const T &value) {
-    if (current_length == allocated_length) {
+    if (current_length == allocated_length) [[unlikely]] {
       size_t new_allocated_length = allocated_length * 2;
       T *new_raw_beg = alloc.allocate(new_allocated_length);
       for (size_t i = 0; i < current_length; ++i) {
@@ -506,11 +514,12 @@ class vector {
    * throw container_is_empty if size() == 0
    */
   void pop_back() {
-    if (current_length == 0) throw container_is_empty();
+    if (current_length == 0) [[unlikely]]
+      throw container_is_empty();
     std::allocator_traits<decltype(alloc)>::destroy(alloc, raw_end - 1);
     raw_end--;
     current_length--;
-    if (current_length != 0 && current_length <= allocated_length / 4) {
+    if (current_length != 0 && current_length <= allocated_length / 4) [[unlikely]] {
       size_t new_allocated_length = allocated_length / 2;
       T *new_raw_beg = alloc.allocate(new_allocated_length);
       for (size_t i = 0; i < current_length; ++i) {