Различия в создании shared_ptr через конструктор и make_shared.

gusenov · gusenov · commit ff8e93e9d5e1 · 2020-07-25T14:31:49.000+06:00
diff --git a/README.md b/README.md
@@ -232,6 +232,7 @@
 - [Сброс std::shared_ptr](smart-ptr/shared_ptr/shared-ptr-reset)
 - [Удаление элемента из std::vector<std::shared_ptr<…>>](smart-ptr/shared_ptr/vec-with-shared-ptr-items)
 - [std::shared_ptr не вызывающий деструктор](smart-ptr/shared_ptr/null-deleter)
+- [Различия в создании shared_ptr через конструктор и make_shared](smart-ptr/shared_ptr/shared_ptr-vs-make_shared)
 
 ## std::weak_ptr
 
diff --git a/smart-ptr/shared_ptr/shared_ptr-vs-make_shared/.gitignore b/smart-ptr/shared_ptr/shared_ptr-vs-make_shared/.gitignore
@@ -0,0 +1,37 @@
+# ---------------------------------------------------------------------------
+# https://github.com/github/gitignore/blob/master/C++.gitignore
+
+# Prerequisites
+*.d
+
+# Compiled Object files
+*.slo
+*.lo
+*.o
+*.obj
+
+# Precompiled Headers
+*.gch
+*.pch
+
+# Compiled Dynamic libraries
+*.so
+*.dylib
+*.dll
+
+# Fortran module files
+*.mod
+*.smod
+
+# Compiled Static libraries
+*.lai
+*.la
+*.a
+*.lib
+
+# Executables
+*.exe
+*.out
+*.app
+
+# ---------------------------------------------------------------------------
diff --git a/smart-ptr/shared_ptr/shared_ptr-vs-make_shared/main.cc b/smart-ptr/shared_ptr/shared_ptr-vs-make_shared/main.cc
@@ -0,0 +1,71 @@
+#include <memory>
+#include <exception>
+#include <iostream>
+#include <tuple>
+
+struct IShape;
+using IShape_S = std::shared_ptr<IShape>;
+using IShape_W = std::weak_ptr<IShape>;
+
+struct IShape {
+    virtual ~IShape() = default;
+    virtual IShape_S shared() = 0;
+    virtual IShape_W weak() = 0;
+};
+
+class Circle : public std::enable_shared_from_this<Circle>,
+               public IShape
+{
+public:
+    ~Circle() override = default;
+    IShape_S shared() override {
+        return shared_from_this();
+    }
+    IShape_W weak() override {
+        return weak_from_this();
+    }
+};
+
+enum class ShapeType {
+    Circle
+};
+
+class ShapeFactory
+{
+public:
+    static IShape* MakeShape(ShapeType shapeType) {
+        switch (shapeType) {
+        case ShapeType::Circle:
+            return new Circle;
+        default:
+            return nullptr;
+        }
+        assert(false);
+    }
+};
+
+int main(int argc, char const* argv[]) {
+    {
+        auto circle = IShape_S(ShapeFactory::MakeShape(ShapeType::Circle));  // !
+        assert(circle->weak().expired());  // TRUE
+        try {
+            assert(circle->shared());
+        } catch (std::exception& e) {
+            std::cout << e.what() << std::endl;  // bad_weak_ptr
+        }
+    }
+
+    {
+        IShape_S circle = std::make_shared<Circle>();
+        assert(!circle->weak().expired());  // TRUE
+        assert(circle->shared());  // TRUE
+    }
+    
+    std::pair my_pair1(123, "abc");
+    auto my_pair2 = std::make_pair(123, "a");
+        
+    return 0;
+}
+
+// При создании shared_ptr через конструктор ему можно передать указатель на интерфейс.
+// make_shared явно требует инстанцируемый класс.
diff --git a/smart-ptr/shared_ptr/shared_ptr-vs-make_shared/run.sh b/smart-ptr/shared_ptr/shared_ptr-vs-make_shared/run.sh
@@ -0,0 +1,7 @@
+#!/bin/bash
+
+EXE_FILE="./program.out"
+
+[ -f "$EXE_FILE" ] && rm "$EXE_FILE"
+
+clang++ --std=c++17 main.cc -o "$EXE_FILE" && "$EXE_FILE"
