Bug 4331 – Struct invariants not called

Struct invariants are useful to restrict the number of possible states of a struct instance. But there are situations where they are not called&run. This D2 program compiles and runs with no errors with 2.047: struct Foo { int x; invariant() { assert(x > 0); } } void main() { Foo f = Foo(-10); } To avoid this I can see two possible solutions: 1) When a struct is initialized through the built-in constructor using user-specified values, as in this case, the compiler can call the invariant() at the end of the initialization. So this code can assert at run-time (or even at compile-time if the compiler is smart) and avoid possible bugs. 2) If the precedent option is not possible, then the compiler has no way to enforce the invariant of this struct Foo (calling f.__invariant() from user code is not a solution). There is no point to keep an invariant if D never enforces it, it's bad to give a false sense of security to the programmer. So the compiler can refuse an invariant at compile-time where it can't be enforced, with an error message.

The StructBodyDeclaration syntax (both D1 and D2) includes Invariant. Therefore the code is legal, and the bug is that the compiler ignores it.

*** This issue has been marked as a duplicate of issue 519 ***