## digitalmars.D.learn - typeid() after const/immutable qualifiers

Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
```In TDPL, page 289 & 299, there's this code (I've modified the names slightly)
and explanation:

struct A
{
const(int[]) c;
immutable(int[]) i;
}

import std.stdio;

unittest
{
const(A) const_a;
immutable(A) immu_b;
}

A short version of the explanation:

"if qualifiers would apply blindly, the types would be:

const_a.c == const(const(int[]))
const_a.i == const(immutable(int[]))

immu_b.c == immutable(const(int[])).
immu_b.i == immutable(immutable(int[])).

When two qualifiers are identical, they are collapsed into one, otherwise
const(immutable(T)) and immutable(const(T)) are both collapsed into
immutable(T)"

From my interpretation, that would mean the types are now:

const_a.c == const(int[])
const_a.i == immutable(int[])

immu_b.c == immutable(int[])
immu_b.i == immutable(int[])

Am I correct so far?

Well first of all, DMD doesn't actually print it out simple qualifiers when
arrays are used, for example:

const(int[]) x;
writeln(typeid(x));

Writes:
const(const(int)[])

Which is fine, both x and it's contents are const so it's the correct output.

The second thing which I'm actually puzzled by, is why I'm getting typeid()
return the same qualifiers as defined in the struct. Here's some simplified
code with using basic types, not arrays:

struct A
{
const(int) c;
immutable(int) i;
}

import std.stdio;

unittest
{
const(A) const_a;
immutable(A) immu_b;

writeln("const_a.c == ", typeid(const_a.c));
writeln("const_a.i == ", typeid(const_a.i));

writeln("immu_b.c == ", typeid(immu_b.c));
writeln("immu_b.i == ", typeid(immu_b.i));
}

void main()
{

}

Writes:
const_a.c == const(int)
const_a.i == immutable(int)

immu_b.c == const(int)
immu_b.i == immutable(int)

const_a.c == const(int)
const_a.i == immutable(int)

immu_b.c == immutable(int)  // immu_b.c is now immutable
immu_b.i == immutable(int)

AFAIK immutable propagates to all fields of the struct, so const c should be an
immutable now?
```
Aug 19 2010
Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
```Btw, should I skip trying to use inout at all for now? I've read some posts
saying that it's awfully broken, and the example of inout in TDPL doesn't work..

Andrej Mitrovic Wrote:

snip

```
Aug 19 2010
"Steven Schveighoffer" <schveiguy yahoo.com> writes:
```On Thu, 19 Aug 2010 12:47:45 -0400, Andrej Mitrovic
<andrej.mitrovich gmail.com> wrote:

Btw, should I skip trying to use inout at all for now? I've read some
posts saying that it's awfully broken, and the example of inout in TDPL
doesn't work..

Yes.  I have expressed the cases that inout should deal with in bug
http://d.puremagic.com/issues/show_bug.cgi?id=3748

-Steve
```
Aug 23 2010
bearophile <bearophileHUGS lycos.com> writes:
```Andrej Mitrovic:
Well first of all, DMD doesn't actually print it out simple qualifiers when
arrays are used, for example:

I have an open bug report on this.

Bye,
bearophile
```
Aug 19 2010
Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
```Good to hear. I was almost going to open an enhancement request. :)

bearophile Wrote:

Andrej Mitrovic:
Well first of all, DMD doesn't actually print it out simple qualifiers when
arrays are used, for example:

I have an open bug report on this.

Bye,
bearophile

```
Aug 19 2010