Added concepts example

Grzegorz Jabłoński
1 parent f264a977
Showing 2 changed files with 49 additions and 1 deletions
examples08/01-template/makefile
examples08/01-template/minimum_concepts.cpp
-all: minimum swap1 swap2 bubblesort
+all: minimum minimum_concepts swap1 swap2 bubblesort
 minimum: minimum.o
 	g++ -g -Wall -pedantic $^ -o $@
@@ -6,6 +6,12 @@ minimum: minimum.o
 minimum.o: minimum.cpp
 	g++ -g -c -Wall -pedantic $< -o $@
+minimum_concepts: minimum_concepts.o
+	g++ -g -Wall -pedantic $^ -o $@
+
+minimum_concepts.o: minimum_concepts.cpp
+	g++ -std=c++20 -g -c -Wall -pedantic $< -o $@
+
 swap1: swap1.o
 	g++ -g -Wall -pedantic $^ -o $@
+#include <iostream>
+#include <string>
+#include <concepts>
+
+using namespace std;
+
+template <class T> 
+concept LessComparable = requires(const T l, const T r, bool res)
+{
+    res = (l < r);
+};
+
+template <class T> T minimum(T x, T y) requires std::constructible_from<T, const T&> && LessComparable<T>
+{
+    if (x < y)
+        return x;
+    else
+        return y;
+}
+
+class NotComparable
+{
+};
+
+class NotCopyConstructible
+{
+  public:
+    NotCopyConstructible(){};
+    NotCopyConstructible(const NotCopyConstructible&) = delete;
+    friend bool operator<(NotCopyConstructible, NotCopyConstructible){return true;};
+};
+
+int main()
+{
+    int x = 50, y = 30;
+    string a = "hello", b = "goodbye";
+    cout << "minimum for ints " << minimum(x, y) << endl;
+    cout << "minimum for strings " << minimum(a, b) << endl;
+//    minimum(NotComparable(), NotComparable());
+//    minimum(NotCopyConstructible(), NotCopyConstructible());
+
+}