Question

immutable class Foo
{
    void bar()
    {
    }
}

void main()
{
    auto x = new Foo();
    x.bar();
    // Error: function test.Foo.bar () immutable is not callable
    //         using argument types ()
}

What do I have to change in the program so that x.bar() compiles? Does x have the wrong type?

Answer 1

Looks like a bug. x is inferred to have the type Foo, which although is an immutable class, it is treated as if a mutable variable, which caused x.bar() to fail because bar() is an immutable method.

A workaround is to provide an empty immutable constructor function,

immutable class Foo
{
    void bar()
    {
    }

    immutable this() {}    // <---
}

which caused the new Foo() expression to return an immutable(Foo).