Add GENERATE_COPY and GENERATE_VAR capturing generator macros

examples/310-Gen-VariablesInGenerators.cpp

@@ -8,41 +8,6 @@
 
 #include <catch2/catch.hpp>
 
-#include <random>
-
-// Lets start by implementing a parametrizable double generator
-class RandomDoubleGenerator : public Catch::Generators::IGenerator<double> {
-    std::minstd_rand m_rand;
-    std::uniform_real_distribution<> m_dist;
-    double current_number;
-public:
-
-    RandomDoubleGenerator(double low, double high):
-        m_rand(std::random_device{}()),
-        m_dist(low, high)
-    {
-        static_cast<void>(next());
-    }
-
-    double const& get() const override;
-    bool next() override {
-        current_number = m_dist(m_rand);
-        return true;
-    }
-};
-
-// Avoids -Wweak-vtables
-double const& RandomDoubleGenerator::get() const {
-    return current_number;
-}
-
-
-// Also provide a nice shortcut for creating the generator
-Catch::Generators::GeneratorWrapper<double> random(double low, double high) {
-    return Catch::Generators::GeneratorWrapper<double>(std::unique_ptr<Catch::Generators::IGenerator<double>>(new RandomDoubleGenerator(low, high)));
-}
-
-
 TEST_CASE("Generate random doubles across different ranges",
           "[generator][example][advanced]") {
     // Workaround for old libstdc++
@@ -55,16 +20,12 @@ TEST_CASE("Generate random doubles across different ranges",
     }));
 
     // This will not compile (intentionally), because it accesses a variable
-    // auto number = GENERATE(take(50, random(r.first, r.second)));
-    
-    // We have to manually register the generators instead
-    // Notice that we are using value capture in the lambda, to avoid lifetime issues
-    auto number = Catch::Generators::generate( CATCH_INTERNAL_LINEINFO,
-        [=]{
-            using namespace Catch::Generators;
-            return makeGenerators(take(50, random(std::get<0>(r), std::get<1>(r))));
-        }
-    );
+    // auto number = GENERATE(take(50, random(std::get<0>(r), std::get<1>(r))));
+
+   // GENERATE_COPY copies all variables mentioned inside the expression
+   // thus this will work.
+    auto number = GENERATE_COPY(take(50, random(std::get<0>(r), std::get<1>(r))));
+
     REQUIRE(std::abs(number) > 0);
 }
 

examples/311-Gen-CustomCapture.cpp

@@ -0,0 +1,41 @@
+// 311-Gen-CustomCapture.cpp
+// Shows how to provide custom capture list to the generator expression
+
+// Note that using variables inside generators is dangerous and should
+// be done only if you know what you are doing, because the generators
+// _WILL_ outlive the variables. Also, even if you know what you are
+// doing, you should probably use GENERATE_COPY or GENERATE_REF macros
+// instead. However, if your use case requires having a
+// per-variable custom capture list, this example shows how to achieve
+// that.
+
+#include <catch2/catch.hpp>
+
+TEST_CASE("Generate random doubles across different ranges",
+          "[generator][example][advanced]") {
+    // Workaround for old libstdc++
+    using record = std::tuple<double, double>;
+    // Set up 3 ranges to generate numbers from
+    auto r1 = GENERATE(table<double, double>({
+        record{3, 4},
+        record{-4, -3},
+        record{10, 1000}
+    }));
+
+    auto r2(r1);
+    
+    // This will take r1 by reference and r2 by value.
+    // Note that there are no advantages for doing so in this example,
+    // it is done only for expository purposes.
+    auto number = Catch::Generators::generate( CATCH_INTERNAL_LINEINFO,
+        [&r1, r2]{
+            using namespace Catch::Generators;
+            return makeGenerators(take(50, random(std::get<0>(r1), std::get<1>(r2))));
+        }
+    );
+
+    REQUIRE(std::abs(number) > 0);
+}
+
+// Compiling and running this file will result in 150 successful assertions
+

examples/CMakeLists.txt

@@ -47,6 +47,7 @@ set( SOURCES_IDIOMATIC_TESTS
     300-Gen-OwnGenerator.cpp
     301-Gen-MapTypeConversion.cpp
     310-Gen-VariablesInGenerators.cpp
+    311-Gen-CustomCapture.cpp
 )
 
 # main-s for reporter-specific test sources: