RNGScope minor refactoring

examples/ex_rng_scope.cpp

@@ -1,30 +1,33 @@
-#include <iostream>
+
 #include <igraph.hpp>
-#include "ex_vector_print.hpp"
+#include <iostream>
+
+// This example illustrates the use of ig::RNGScope, which provides a localized
+// random state within the current scope.
 
 int main() {
     // Check that we can influence the RNG.
     {
-        ig::RNGScope filled(1000);
+        ig::RNGScope filled(42);
         std::cout << "New RNG scope:" << std::endl;
-        std::cout << "  Draw from [0, 100]: " << igraph_rng_get_integer(igraph_rng_default(), 0, 100) << std::endl;
-        std::cout << "  Draw from [0, 100]: " << igraph_rng_get_integer(igraph_rng_default(), 0, 100) << std::endl;
+        std::cout << "  Draw from [0, 100]: " << RNG_INTEGER(0, 100) << std::endl;
+        std::cout << "  Draw from [0, 100]: " << RNG_INTEGER(0, 100) << std::endl;
     }
 
     // Check that the destructor correctly unsets the RNG.
     {
-        ig::RNGScope filled(1000);
+        ig::RNGScope filled(42);
         std::cout << "New RNG scope:" << std::endl;
-        std::cout << "  Draw from [0, 100]: " << igraph_rng_get_integer(igraph_rng_default(), 0, 100) << std::endl;
+        std::cout << "  Draw from [0, 100]: " << RNG_INTEGER(0, 100) << std::endl;
 
         {
-            ig::RNGScope nested; // uses a default seed and type.
+            ig::RNGScope nested; // uses a default type and a seed generated via std::random_device
             std::cout << "  New RNG scope:" << std::endl;
-            std::cout << "    Draw from [0, 100]: " << igraph_rng_get_integer(igraph_rng_default(), 0, 100) << std::endl;
-            std::cout << "    Draw from [0, 100]: " << igraph_rng_get_integer(igraph_rng_default(), 0, 100) << std::endl;
+            std::cout << "    Draw from [0, 100]: " << RNG_INTEGER(0, 100) << std::endl;
+            std::cout << "    Draw from [0, 100]: " << RNG_INTEGER(0, 100) << std::endl;
         }
 
-        std::cout << "  Draw from [0, 100]: " << igraph_rng_get_integer(igraph_rng_default(), 0, 100) << std::endl;
+        std::cout << "  Draw from [0, 100]: " << RNG_INTEGER(0, 100) << std::endl;
     }
 
     return 0;

include/igraph.hpp

@@ -11,6 +11,7 @@
 #include <cassert>
 #include <complex>
 #include <iterator>
+#include <random>
 #include <stdexcept>
 #include <type_traits>
 #include <utility>

include/rng_scope.hpp

@@ -1,41 +1,40 @@
+
 class RNGScope {
+    igraph_rng_t *previous;
+    igraph_rng_t current;
+
+    constexpr const static igraph_rng_type_t *default_type = &igraph_rngtype_pcg32;
+
 public:
-    RNGScope(igraph_uint_t seed) : RNGScope(seed, &igraph_rngtype_pcg32) {}
+    explicit RNGScope(igraph_uint_t seed) : RNGScope(seed, default_type) {}
 
-    RNGScope(igraph_uint_t seed, const igraph_rng_type_t* type) {
+    RNGScope(igraph_uint_t seed, const igraph_rng_type_t *type) {
         check(igraph_rng_init(&current, type));
 
-        auto errcode = igraph_rng_seed(&current, seed);
+        igraph_error_t errcode = igraph_rng_seed(&current, seed);
         if (errcode != IGRAPH_SUCCESS) {
             igraph_rng_destroy(&current);
             throw Exception(errcode);
         }
 
-        previous = *(igraph_rng_default());
+        // TODO for igraph 1.0 where igraph_rng_set_default() returns the previous generator.
+        previous = igraph_rng_default();
         igraph_rng_set_default(&current);
     }
 
-    RNGScope(const igraph_rng_type_t* type) {
-        check(igraph_rng_init(&current, type));
-        previous = *(igraph_rng_default());
-        igraph_rng_set_default(&current);
-    }
+    explicit RNGScope(const igraph_rng_type_t *type) : RNGScope(std::random_device{}(), type) { }
 
-    RNGScope() : RNGScope(&igraph_rngtype_pcg32) {}
+    RNGScope() : RNGScope(default_type) { }
 
 public:
-    // We shouldn't be copying or moving an RNGscope object, as this defeats the logic provided by scoping.
-    RNGScope(const RNGScope&) = delete;
-    RNGScope& operator=(const RNGScope&) = delete;
-    RNGScope(RNGScope&&) = delete;
-    RNGScope& operator=(RNGScope&&) = delete;
+    // We shouldn't be copying or moving an RNGScope object, as this defeats the logic provided by scoping.
+    RNGScope(const RNGScope &) = delete;
+    RNGScope & operator = (const RNGScope&) = delete;
+    RNGScope(RNGScope &&) = delete;
+    RNGScope & operator = (RNGScope &&) = delete;
 
     ~RNGScope() {
-        igraph_rng_set_default(&previous);
+        igraph_rng_set_default(previous);
         igraph_rng_destroy(&current);
     }
-
-private:
-    igraph_rng_t previous;
-    igraph_rng_t current;
 };