[Issue 13428] Add template to perform appropriate substitution for inout when it appears in a type

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=13428

--- Comment #3 from Simen Kjaeraas <simen.kjaras at gmail.com> ---
I revisited this today, and realized it does not handle mixed qualifiers, like
inout(const(int)*). As this is a rather big oversight, here's an improved
implementation:

template SubstituteInout(FromType, ToType)
{
    alias Modifiers(T) = CopyTypeQualifiers!(FromType, T);
    alias Next(T) =      SubstituteInout!(FromType, T);

         static if (is(ToType U ==          immutable U)) alias SubstituteInout
=    immutable            Next!U;
    else static if (is(ToType U == shared inout const U)) alias SubstituteInout
= shared const Modifiers!(Next!U);
    else static if (is(ToType U == shared inout       U)) alias SubstituteInout
= shared       Modifiers!(Next!U);
    else static if (is(ToType U == shared       const U)) alias SubstituteInout
= shared const            Next!U;
    else static if (is(ToType U == shared             U)) alias SubstituteInout
= shared                  Next!U;
    else static if (is(ToType U ==        inout const U)) alias SubstituteInout
=        const Modifiers!(Next!U);
    else static if (is(ToType U ==        inout       U)) alias SubstituteInout
=              Modifiers!(Next!U);
    else static if (is(ToType U ==              const U)) alias SubstituteInout
=        const            Next!U;
    else static if (is(ToType U ==       U*            )) alias SubstituteInout
=                         Next!U*;
    else static if (is(ToType U ==       U[]           )) alias SubstituteInout
=                         Next!U[];
    else static if (is(ToType U ==       U[N], size_t N)) alias SubstituteInout
=                         Next!U[N];
    else static if (is(ToType U ==       U[K],        K)) alias SubstituteInout
=                         Next!U[Next!K];
    else                                                  alias SubstituteInout
= ToType;
}

unittest {
    static assert(is(SubstituteInout!(const(string), int) == int));
    static assert(is(SubstituteInout!(const(string), inout(int)[]) ==
const(int)[]));
    static assert(is(SubstituteInout!(const(string), inout(int)) ==
const(int)));
    static assert(is(SubstituteInout!(const(string), inout(int)*[][3][int]) ==
const(int)*[][3][int]));
    static assert(is(SubstituteInout!(const(string), inout(int)[inout(string)])
== const(int)[const(string)]));

    static assert(is(SubstituteInout!(const(int), inout(const(int)*)) ==
const(int*)));
    static assert(is(SubstituteInout!(int, inout(const(int)*)) ==
const(int)*));
}

--