Update modules chapter for 2025.

Author: hageboeck

talk/expert/modules.tex

@@ -29,10 +29,10 @@
   \frametitlecpp[20]{Writing modules}
   \begin{exampleblock}{ratio.cpp}
     \begin{cppcode*}{}
-      export module math;
+      export module math;   // module declaration
       import <string>;
       namespace utils { // ns. and module names orthogonal
-        export struct Ratio { float num, denom; };
+        export struct Ratio { int num, denom; };
         export std::string toString(const Ratio& r) { ... }
         void normalize(Ratio& r) { ... } // not exported
       }
@@ -112,11 +112,11 @@
   \begin{exampleblock}{ratio.cpp}
     \begin{cppcode*}{}
       export module math;
-      struct Ratio { float num, denom; };
+      struct Ratio { int num, denom; };
       export Ratio golden() { ... } // golden is visible
     \end{cppcode*}
   \end{exampleblock}
-  \begin{exampleblock}{main.cpp}
+  \begin{exampleblockGB}{main.cpp}{https://godbolt.org/z/n95rdxPdos}{Modules example}
     \begin{cppcode*}{}
       import math;
       import <iostream>;
@@ -129,7 +129,7 @@
         R r2{1.f, 3.f};     // OK
       }
     \end{cppcode*}
-  \end{exampleblock}
+  \end{exampleblockGB}
 \end{frame}
 
 \begin{frame}[fragile]
@@ -191,7 +191,7 @@
   \end{block}
   \begin{exampleblock}{Interface}
     \begin{cppcode*}{}
-      export module math;
+      export module math; // Module interface unit declaration
 
       export struct S { ... };
       export S f();
@@ -201,7 +201,7 @@
     \begin{cppcode*}{}
       module;
       #include <cassert>
-      module math;
+      module math;        // Module implementation unit
       import <string>;
 
       S f() { ... }
@@ -348,19 +348,20 @@
   % see: Minimal module support for the standard library http://wg21.link/P2412
   \begin{block}{Standard library modules}
     \begin{itemize}
-      \item Use \cppinline|import std;| for the entire C++ standard library. Basically everything in namespace \cppinline|std|.
+      \item Use \cppinline|import std;| for the entire C++ standard library.
       \begin{itemize}
       \item E.g.\ \cppinline{memcpy(a, b, n)}, \cppinline{sqrt(val)}, \cppinline{uint32_t}
       \item Note that you need to prefix with \cppinline{std::}
+      \item Currently, support is not great (see later)
       \end{itemize}
-      \item Use \cppinline|import std.compat;| for the entire C and C++ standard library
+      \item \cppinline|import std.compat;| for the C and C++
       \item No macros are exported. For these, you still need to include the corresponding headers.
       \begin{cppcode*}{}
         import std;        // everything C++
         #include <cassert> // for assert()
         #include <climits> // for e.g. CHAR_BIT
       \end{cppcode*}
-      \item Definition of further, smaller modules of the standard library is in progress (e.g.\ fundamentals, containers, networking, etc.)
+      \item Definition of further, smaller modules of the standard library is in progress
     \end{itemize}
   \end{block}
 \end{frame}
@@ -405,7 +406,7 @@
     \frametitlecpp[20]{Automatic include to import translation}
     \begin{block}{Importable headers}
       \begin{itemize}
-      \item A header file which can successfully be either included or imported is called ``importable''
+      \item A header file which can either be included or imported is called ``importable''
       \begin{itemize}
         \item I.e.\ the header does not require setup of preprocessor state before inclusion
       \end{itemize}
@@ -607,38 +608,23 @@
     \frametitlecpp[20]{Build system}
     \begin{block}{Status}
       \begin{itemize}
-        \item Dependency scanner since clang 16: \texttt{clang-scan-deps}
-        \item Experimental module support in cmake since 3.26, uses \texttt{clang-scan-deps}, many fixes in later versions % see: https://discourse.cmake.org/t/c-20-modules-update/7330/24 and https://youtu.be/c563KgO-uf4?si=HUpnSivtDxvBoTr3&t=3592
-        \item MSBuild (Windows) fully handles dependency scanning
-        \item \cppinline{g++ a.cpp b.cpp ...} ``just works'', must be one line though
-        \item \href{https://wg21.link/p1602}{Experimental extensions to GNU make} exist to grow dependency graph on the fly while modules are discovered
-        \item Header units unsupported in all build systems (May 2023) % See talk: https://youtu.be/_LGR0U5Opdg?si=yQoCYD2yGFhi_vs6&t=3768
-        \item C++23: \cppinline{import std;} supported in MSVC, partially in clang
+        \item Build systems:
         \begin{itemize}
-          \item GCC/clang/MSVC also plan support in C++20 % see: https://github.com/microsoft/STL/issues/3945
+          \item Dependency scanner since clang 16: \texttt{clang-scan-deps}
+          \item Cmake support in v3.28 (\href{https://cmake.org/cmake/help/latest/manual/cmake-cxxmodules.7.html}{documentation})
+          \item MSBuild (Windows) fully handles dependency scanning
+          \item \href{https://wg21.link/p1602}{Experimental extensions to GNU make}
         \end{itemize}
-      \end{itemize}
-    \end{block}
-\end{frame}
-
-\begin{frame}[fragile]
-    \frametitlecpp[20]{Building modules (g++)}
-    \begin{block}{Case study: g++}
-      \begin{itemize}
-        \item BMI is called CMI (compiled module interfaces)
-        \item By default, g++ caches CMIs in subdirectory \texttt{./gcm.cache}
-        \item Uses a \href{https://wg21.link/P1184}{module mapper} to resolve imports, which specifies a protocol and uses a central server for module maintenance
-        \item Each module needs to be built before it can be imported
-        \begin{itemize}
-          \item {\footnotesize \cppinline{g++ -std=c++20 -fmodules-ts -c ratio.cpp -o ratio.o}}
-          \item Generates \texttt{ratio.o} and \texttt{./gcm.cache/ratio.gcm} (CMI)
-        \end{itemize}
-        \item Each header unit needs to be built before it can be imported
+        \item \cppinline{g++ a.cpp b.cpp ...} ``just works'', must be one line though
+        \item C++23: \cppinline{import std;} supported in MSVC, partially in clang and gcc
+          \begin{itemize}
+            \item The standard library module currently has to be compiled manually (\href{https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=7db55c0ba1baaf0e323ef7f9ef8c9cda077d40e9}{see gcc commit in 2024},
+            \href{https://0xstubs.org/using-the-c23-std-module-with-gcc-15/}{gcc-15 recipe}, \href{https://0xstubs.org/using-the-c23-std-module-with-clang-18/}{clang-18 recipe})
+            \item GCC/clang/MSVC also plan support in C++20 % see: https://github.com/microsoft/STL/issues/3945
+          \end{itemize}
+        \item Header units unsupported (May 2023) % See talk: https://youtu.be/_LGR0U5Opdg?si=yQoCYD2yGFhi_vs6&t=3768
         \begin{itemize}
-          \item {\footnotesize \cppinline{g++ -std=c++20 -fmodules-ts -x c++-system-header vector}}
-          \item Generates e.g.\ \texttt{./gcm.cache/usr/include/c++/11/vector.gcm} (CMI)
-          \item {\footnotesize \cppinline{g++ -std=c++20 -fmodules-ts -x c++-header ratio.h}}
-          \item Generates e.g.\ \texttt{./gcm.cache/,/ratio.h.gcm} (CMI)
+          \item Standard library header units possible in gcc11 and MSVC (2025)
         \end{itemize}
       \end{itemize}
     \end{block}
@@ -658,7 +644,7 @@
     \begin{exampleblock}{Guidance for tomorrow}
       \begin{itemize}
         \item Start writing modules when your users have \cpp20
-        \item Maybe import standard headers when \cpp20 is available
+        \item Maybe import standard headers when compilers fully support \cpp20
         \item Start using \cppinline{import std;} when available
         \item Future of header units unclear (implementation difficulties)
       \end{itemize}