return a pointer from the "at" methods (which is nullptr on non-existent items)

octa/array.hh

@@ -29,8 +29,14 @@ struct Array {
     T &operator[](Size i) { return p_buf[i]; }
     const T &operator[](Size i) const { return p_buf[i]; }
 
-    T &at(Size i) { return p_buf[i]; }
-    const T &at(Size i) const { return p_buf[i]; }
+    T *at(Size i) {
+        if (!in_range(i)) return nullptr;
+        return &p_buf[i];
+    }
+    const T *at(Size i) const {
+        if (!in_range(i)) return nullptr;
+        return &p_buf[i];
+    }
 
     T &front() { return p_buf[0]; }
     const T &front() const { return p_buf[0]; }

octa/vector.hh

@@ -288,8 +288,14 @@ public:
     T &operator[](Size i) { return p_buf.first()[i]; }
     const T &operator[](Size i) const { return p_buf.first()[i]; }
 
-    T &at(Size i) { return p_buf.first()[i]; }
-    const T &at(Size i) const { return p_buf.first()[i]; }
+    T *at(Size i) {
+        if (!in_range(i)) return nullptr;
+        return &p_buf.first()[i];
+    }
+    const T *at(Size i) const {
+        if (!in_range(i)) return nullptr;
+        return &p_buf.first()[i];
+    }
 
     T &push(const T &v) {
         if (p_len == p_cap) reserve(p_len + 1);

tests/array.cc

@@ -14,8 +14,8 @@ int main() {
     assert(x[0] == 2);
     assert(x[2] == 8);
 
-    assert(x.at(0) == x[0]);
-    assert(x.at(3) == x[3]);
+    assert(*(x.at(0)) == x[0]);
+    assert(*(x.at(3)) == x[3]);
 
     assert(x.size() == 5);
 

tests/vector.cc

@@ -14,8 +14,8 @@ int main() {
     assert(x[0] == 5);
     assert(x[2] == 15);
 
-    assert(x.at(0) == x[0]);
-    assert(x.at(3) == x[3]);
+    assert(*(x.at(0)) == x[0]);
+    assert(*(x.at(3)) == x[3]);
 
     assert(x.data()[0] == x[0]);