diff --git a/README.md b/README.md
index 248db58..7c703dc 100644
--- a/README.md
+++ b/README.md
@@ -1769,13 +1769,13 @@ template < typename T, size_t Size >
 T component(const vec<T, Size>& v, size_t index);
 
 template < typename T, size_t Size >
-vec<T, Size> component(vec<T, Size> v, size_t index, T x);
+vec<T, Size> component(const vec<T, Size>& v, size_t index, T x);
 
 template < typename T, size_t Size >
 vec<T, Size> row(const mat<T, Size>& m, size_t index);
 
 template < typename T, size_t Size >
-mat<T, Size> row(mat<T, Size> m, size_t index, const vec<T, Size>& v);
+mat<T, Size> row(const mat<T, Size>& m, size_t index, const vec<T, Size>& v);
 
 template < typename T, size_t Size >
 vec<T, Size> column(const mat<T, Size>& m, size_t index);
@@ -1783,6 +1783,12 @@ vec<T, Size> column(const mat<T, Size>& m, size_t index);
 template < typename T, size_t Size >
 mat<T, Size> column(const mat<T, Size>& m, size_t index, const vec<T, Size>& v);
 
+template < typename T, size_t Size >
+vec<T, Size> diagonal(const mat<T, Size>& m);
+
+template < typename T, size_t Size >
+mat<T, Size> diagonal(const mat<T, Size>& m, const vec<T, Size>& diagonal);
+
 template < typename T >
 T real(const qua<T>& q);
 
diff --git a/headers/vmath.hpp/vmath_ext.hpp b/headers/vmath.hpp/vmath_ext.hpp
index af55c0f..9c54312 100644
--- a/headers/vmath.hpp/vmath_ext.hpp
+++ b/headers/vmath.hpp/vmath_ext.hpp
@@ -152,9 +152,10 @@ namespace vmath_hpp
     }
 
     template < typename T, std::size_t Size >
-    [[nodiscard]] constexpr vec<T, Size> component(vec<T, Size> v, std::size_t index, T component) {
-        v[index] = component;
-        return v;
+    [[nodiscard]] constexpr vec<T, Size> component(const vec<T, Size>& v, std::size_t index, T component) {
+        vec vv = v;
+        vv[index] = component;
+        return vv;
     }
 
     // row
@@ -165,9 +166,10 @@ namespace vmath_hpp
     }
 
     template < typename T, std::size_t Size >
-    [[nodiscard]] constexpr mat<T, Size> row(mat<T, Size> m, std::size_t index, const vec<T, Size>& row) {
-        m.rows[index] = row;
-        return m;
+    [[nodiscard]] constexpr mat<T, Size> row(const mat<T, Size>& m, std::size_t index, const vec<T, Size>& row) {
+        mat mm = m;
+        mm[index] = row;
+        return mm;
     }
 
     // column
@@ -197,6 +199,31 @@ namespace vmath_hpp
         return impl::column_impl(m, index, column, std::make_index_sequence<Size>{});
     }
 
+    // diagonal
+
+    namespace impl
+    {
+        template < typename T, std::size_t Size, std::size_t... Is >
+        [[nodiscard]] constexpr vec<T, Size> diagonal_impl(const mat<T, Size>& m, std::index_sequence<Is...>) {
+            return { m[Is][Is]... };
+        }
+
+        template < typename T, std::size_t Size, std::size_t... Is >
+        [[nodiscard]] constexpr mat<T, Size> diagonal_impl(const mat<T, Size>& m, const vec<T, Size>& diagonal, std::index_sequence<Is...>) {
+            return { component(m[Is], Is, diagonal[Is])... };
+        }
+    }
+
+    template < typename T, std::size_t Size >
+    [[nodiscard]] constexpr vec<T, Size> diagonal(const mat<T, Size>& m) {
+        return impl::diagonal_impl(m, std::make_index_sequence<Size>{});
+    }
+
+    template < typename T, std::size_t Size >
+    [[nodiscard]] constexpr mat<T, Size> diagonal(const mat<T, Size>& m, const vec<T, Size>& diagonal) {
+        return impl::diagonal_impl(m, diagonal, std::make_index_sequence<Size>{});
+    }
+
     // real
 
     template < typename T >
diff --git a/untests/CMakeLists.txt b/untests/CMakeLists.txt
index 0220203..edc5959 100644
--- a/untests/CMakeLists.txt
+++ b/untests/CMakeLists.txt
@@ -18,7 +18,7 @@ endif()
 
 file(GLOB_RECURSE UNTESTS_SOURCES "*.cpp" "*.hpp")
 add_executable(${PROJECT_NAME} ${UNTESTS_SOURCES})
-target_link_libraries(${PROJECT_NAME} vmath.hpp.singles)
+target_link_libraries(${PROJECT_NAME} vmath.hpp)
 
 target_compile_options(${PROJECT_NAME}
     PRIVATE
diff --git a/untests/vmath_ext_tests.cpp b/untests/vmath_ext_tests.cpp
index 2ca03e0..73eff9c 100644
--- a/untests/vmath_ext_tests.cpp
+++ b/untests/vmath_ext_tests.cpp
@@ -205,6 +205,14 @@ TEST_CASE("vmath/ext/access") {
         STATIC_CHECK(column(imat2(), 1, {3,4}) == imat2(1,3,0,4));
     }
 
+    SUBCASE("diagonal") {
+        STATIC_CHECK(diagonal(imat2(1,2,3,4)) == ivec2(1,4));
+        STATIC_CHECK(diagonal(imat2(1,2,3,4), ivec2(10,40)) == imat2(10,2,3,40));
+
+        STATIC_CHECK(diagonal(imat3(1,2,3,4,5,6,7,8,9)) == ivec3(1,5,9));
+        STATIC_CHECK(diagonal(imat3(1,2,3,4,5,6,7,8,9), ivec3(10,50,90)) == imat3(10,2,3,4,50,6,7,8,90));
+    }
+
     SUBCASE("real") {
         STATIC_CHECK(real(qua{1,2,3,4}) == 4);
         STATIC_CHECK(real(qua{1,2,3,4}, 5) == qua{1,2,3,5});
diff --git a/untests/vmath_fix_tests.cpp b/untests/vmath_fix_tests.cpp
index 5c89095..ab436f2 100644
--- a/untests/vmath_fix_tests.cpp
+++ b/untests/vmath_fix_tests.cpp
@@ -362,10 +362,10 @@ namespace vmath_hpp
 namespace vmath_hpp
 {
     template fix<float> component(const fix2f&, std::size_t);
-    template fix2f component(fix2f, std::size_t, fix<float>);
+    template fix2f component(const fix2f&, std::size_t, fix<float>);
 
     template fix2f row(const fix2x2f&, std::size_t);
-    template fix2x2f row(fix2x2f, std::size_t, const fix2f&);
+    template fix2x2f row(const fix2x2f&, std::size_t, const fix2f&);
 
     template fix2f column(const fix2x2f&, std::size_t);
     template fix2x2f column(const fix2x2f&, std::size_t, const fix2f&);