Assertions: Difference between revisions

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 </pre>
 =={{header|D}}==
+<lang d>import std.exception: enforce;
+int foo(in bool condition) pure nothrow
-<lang d>import std.string;
+in {
-void main() {
+    // Assertions are used in contract programming.
-  int a = readln().chomp().atoi();
-  assert(a == 42, "You did not input 42!");
+    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");
 }</lang>