fix some deprecated methods

meson.build

@@ -3,7 +3,7 @@ project(
   'hack', 
   'cpp', 
   version : '0.0.1', 
-  default_options : ['cpp_std=c++2a']
+  default_options : ['cpp_std=c++20']
 )
 
 add_project_arguments (

src/iterators/associative_ostream_iterator.hpp

@@ -5,8 +5,9 @@
 namespace hack::iterators
 {
   template<typename T>
-  class associative_ostream_iterator : public std::iterator<std::output_iterator_tag, void, void, void, void>
+  class associative_ostream_iterator
   {
+    using iterator_category = std::output_iterator_tag;
     using traits = std::char_traits<char>;
     using ostream_type = std::basic_ostream<char, traits>;
 

src/iterators/sequence_ostream_iterator.hpp

@@ -5,8 +5,9 @@
 namespace hack::iterators
 {
   template<typename T>
-  class sequence_ostream_iterator : public std::iterator<std::output_iterator_tag, void, void, void, void>
+  class sequence_ostream_iterator
   {
+    using iterator_category = std::output_iterator_tag;
     using traits = std::char_traits<char>;
     using ostream_type = std::basic_ostream<char, traits>;
 

src/math/matrix.hpp

@@ -4,6 +4,7 @@
 #include <vector>
 #include <tuple>
 #include <iostream>
+#include <algorithm>
 
 namespace hack::matrix_utils
 {