In DMD 2.053 this code compiles with no errors, because "invariant" is an alias for "immutable" still:


void main() {
    invariant x = 10;
}


But I suggest to remove this alias soon because it causes me some troubles regarding Class/struct/enum invariants. 


DMD v2.053 compiles this with no errors:


struct Foo {
    invariant {}
}
struct Bar {
    invariant
}
class CFoo {
    invariant {}
}
class CBar {
    invariant
}
void main() {}


See bug 4325 for more info.