learn more c++, it never ends

README.adoc

@@ -15496,7 +15496,7 @@ Programs under link:userland/cpp/[] are examples of https://en.wikipedia.org/wik
 * templates
 ** link:userland/cpp/template.cpp[]: basic example
 ** link:userland/cpp/template_class_with_static_member.cpp[]: https://stackoverflow.com/questions/3229883/static-member-initialization-in-a-class-template
-** link:userland/cpp/if_constexpr.cpp[]: C++17 `if constexpr`
+** link:userland/cpp/if_constexpr.cpp[]: C++17 `if constexpr`: https://stackoverflow.com/questions/12160765/if-else-at-compile-time-in-c/54647315#54647315
 * iostream
 ** link:userland/cpp/copyfmt.cpp[]: `std::copyfmt` restores stream state, see also: https://stackoverflow.com/questions/12560291/set-back-default-floating-point-print-precision-in-c/53673686#53673686
 * fstream
@@ -15509,6 +15509,26 @@ Programs under link:userland/cpp/[] are examples of https://en.wikipedia.org/wik
 *** <<algorithms>> contains a benchmark comparison of different c++ containers
 *** link:userland/cpp/set.cpp[]: `std::set` contains unique keys
 
+[[cpp-initialization-types]]
+==== C++ initialization types
+
+OMG this is hell, understand when primitive variables are initialized or not:
+
+* https://stackoverflow.com/questions/3127454/how-do-c-class-members-get-initialized-if-i-dont-do-it-explicitly
+* https://blog.tartanllama.xyz/initialization-is-bonkers/
+
+Intuition:
+
+* direct initialization: a constructor called explicitly with at least one argument: https://en.cppreference.com/w/cpp/language/direct_initialization
+* default initialization: does not initialize primitive types: https://en.cppreference.com/w/cpp/language/default_initialization
+* value initialization: maybe initializes primitive types: https://en.cppreference.com/w/cpp/language/value_initialization
+* zero initialization: initializes primitive types
+
+Good rule:
+
+* initialize every single variable explicitly to prevent the risk of having uninitialized variables due to programmer error (which is easy to get wrong due to insane rules)
+* if you don't define your own default constructor, always `= delete` it instead. This prevents the possibility that variables will be assigned twice due to zero initialization
+
 [[cpp-multithreading]]
 ==== C++ multithreading