Feature: variant2

.github/workflows/publish-conan-branch-package.yml

@@ -12,7 +12,7 @@ jobs:
     with:
       public_artifactory: true
       os: ubuntu-22.04
-      compiler: clang-14
+      compiler: clang-18
       cmake-version: 3.24.0
       conan-version: 2.3.1
     secrets:

CMakeLists.txt

@@ -6,7 +6,7 @@ project(
   DESCRIPTION
     "This template library is a collection of template-oriented code that we, the Data Science Group at UPB, found pretty handy. It contains: `switch_cases` (Use runtime values in compile-time context), `integral_template_tuple` (Create a tuple-like structure that instantiates a template for a range of values), `integral_template_variant` (A wrapper type for `std::variant` guarantees to only contain variants of the form `T<IX>` and `for_{types,values,range}` (Compile time for loops for types, values or ranges))."
   HOMEPAGE_URL "https://dice-research.org/")
-set(POBR_VERSION 1)  # Persisted Object Binary Representation
+set(POBR_VERSION 2)  # Persisted Object Binary Representation
 
 configure_file(${CMAKE_CURRENT_SOURCE_DIR}/cmake/version.hpp.in ${CMAKE_CURRENT_SOURCE_DIR}/include/dice/template-library/version.hpp)
 

README.md

@@ -15,6 +15,7 @@ It contains:
 - `tuple_algorithms`: Some algorithms for iterating tuples
 - `generator`: The reference implementation of `std::generator` from [P2502R2](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2502r2.pdf)
 - `channel`: A single producer, single consumer queue
+- `variant2`: Like `std::variant` but optimized for exactly two types
 
 ## Usage
 
@@ -87,6 +88,11 @@ all generator related things under namespace `std::`.
 A single producer, single consume queue. This can be used to communicate between threads in a more high level
 fashion than a mutex+container would allow.
 
+### `variant2`
+Like `std::variant` but specifically optimized for usage with two types/variants. 
+The internal representation is a `union` of the two types plus a 1 byte (3 state) discriminant.
+Additionally, `visit` does not involve any virtual function calls.
+
 ### Further Examples
 
 Compilable code examples can be found in [examples](./examples). The example build requires the cmake

examples/CMakeLists.txt

@@ -1,5 +1,5 @@
 set(CMAKE_CXX_STANDARD 20)
-set(CMAKE_CXX_STANDARD_REQUIRED True)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
 
 add_executable(examples_for examples_for.cpp)
@@ -72,3 +72,11 @@ target_link_libraries(example_channel
         PRIVATE
         dice-template-library::dice-template-library
 )
+
+add_executable(example_variant2
+        example_variant2.cpp)
+target_link_libraries(example_variant2
+        PRIVATE
+        dice-template-library::dice-template-library
+)
+

examples/example_variant2.cpp

@@ -0,0 +1,41 @@
+#include <cassert>
+#include <string>
+
+#include <dice/template-library/variant2.hpp>
+
+namespace dtl = dice::template_library;
+using namespace std::literals;
+
+int main() {
+	// example adapted from from https://en.cppreference.com/w/cpp/utility/variant
+
+	dtl::variant2<int, float> v;
+	dtl::variant2<int, float> w;
+
+	v = 42; // v contains int
+	int i = dtl::get<int>(v);
+	assert(42 == i); // succeeds
+	w = dtl::get<int>(v);
+	w = dtl::get<0>(v); // same effect as the previous line
+	w = v; // same effect as the previous line
+
+	//  dtl::get<double>(v); // error: no double in [int, float]
+	//  dtl::get<3>(v);      // error: valid index values are 0 and 1
+
+	try {
+		(void) dtl::get<float>(w); // w contains int, not float: will throw
+	}
+	catch (dtl::bad_variant_access const &ex) {
+		assert(ex.what() == "bad variant access"s);
+	}
+
+	dtl::variant<std::string> x("abc");
+	// converting constructors work when unambiguous
+	x = "def"; // converting assignment also works when unambiguous
+
+	dtl::variant<std::string, void const*> y("abc");
+	// casts to void const* when passed a char const*
+	assert(dtl::holds_alternative<void const*>(y)); // succeeds
+	y = "xyz"s;
+	assert(dtl::holds_alternative<std::string>(y)); // succeeds
+}