[Issue 15660] breack "immutable" with pure function and mutable params

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=15660

--- Comment #1 from Iakh <iaktakh at gmail.com> ---
Also this works

import std.stdio;

class A
{
    int i;
}

class B : A {}
struct S
{
    A a;

    auto f() pure @safe
    {
        B b = new B;
        a = b;
        return b;
    }
}

void main() @safe
{
    S s;
    immutable a = s.f();
    A b = s.a;
    writeln(a.i);
    b.i = 1;
    writeln(a.i);
}

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