Data commit

Task/Assertions/D/assertions.d

@@ -0,0 +1,36 @@
+import std.exception: enforce;
+
+int foo(in bool condition) pure nothrow
+in {
+    // Assertions are used in contract programming.
+    assert(condition);
+} out(result) {
+    assert(result > 0);
+} body {
+    if (condition)
+        return 42;
+
+    // assert(false) is never stripped from the code, it generates an
+    // error in debug builds, and it becomes a HALT instruction in
+    // -release mode.
+    //
+    // It's used as a mark by the D type system. If you remove this
+    // line the compiles gives an error:
+    //
+    // Error: function assertions.foo no return exp;
+    //   or assert(0); at end of function
+    assert(false, "This can't happen.");
+}
+
+void main() pure {
+    int x = foo(true);
+
+    // A regular assertion, it throws an error.
+    // Use -release to disable it.
+    // It can be used in nothrow functions.
+    assert(x == 42, "x is not 42");
+
+    // This throws an exception and it can't be disabled.
+    // There are some different versions of this lazy function.
+    enforce(x == 42, "x is not 42");
+}