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digitalmars.D.learn - Very strange compilation error

reply "Jack Applegame" <japplegame gmail.com> writes:
I don't understand why this code doesn't compile:

http://dpaste.dzfl.pl/dfd8df7f80ad
Oct 15 2014
next sibling parent reply "John Colvin" <john.loughran.colvin gmail.com> writes:
On Wednesday, 15 October 2014 at 19:29:27 UTC, Jack Applegame 
wrote:

 I don't understand why this code doesn't compile:

 http://dpaste.dzfl.pl/dfd8df7f80ad


that should be immutable(ubyte)[] not immutable ubyte[] which is 
equivalent to immutable(ubyte[]). You can't overwrite immutable 
data, hence the error.
Oct 15 2014
parent reply Nils =?UTF-8?B?Qm/Dn3VuZw==?= <nilsbossung googlemail.com> writes:
On Wednesday 15 October 2014 22:13, John Colvin wrote:


 On Wednesday, 15 October 2014 at 19:29:27 UTC, Jack Applegame
 wrote:

 I don't understand why this code doesn't compile:

 http://dpaste.dzfl.pl/dfd8df7f80ad


 
 that should be immutable(ubyte)[] not immutable ubyte[] which is
 equivalent to immutable(ubyte[]). You can't overwrite immutable
 data, hence the error.


Then

  Foo1 foo1; foo1 = Foo1(); // compiles

shouldn't compile either.
Oct 15 2014
parent "John Colvin" <john.loughran.colvin gmail.com> writes:
On Wednesday, 15 October 2014 at 21:28:05 UTC, Nils Boßung wrote:

 On Wednesday 15 October 2014 22:13, John Colvin wrote:


 On Wednesday, 15 October 2014 at 19:29:27 UTC, Jack Applegame
 wrote:

 I don't understand why this code doesn't compile:

 http://dpaste.dzfl.pl/dfd8df7f80ad


 
 that should be immutable(ubyte)[] not immutable ubyte[] which 
 is
 equivalent to immutable(ubyte[]). You can't overwrite immutable
 data, hence the error.


 Then

   Foo1 foo1; foo1 = Foo1(); // compiles

 shouldn't compile either.


Good point. That's an accepts-invalid IMO.

Nonetheless:
union { string a; immutable ubyte[] b; }
is broken, it is effectively casting away immutability.
union { string a; immutable(ubyte)[] b; } is the correct approach.
Oct 16 2014
prev sibling parent Nils =?UTF-8?B?Qm/Dn3VuZw==?= <nilsbossung googlemail.com> writes:
On Wednesday 15 October 2014 21:29, Jack Applegame wrote:


 I don't understand why this code doesn't compile:
 
 http://dpaste.dzfl.pl/dfd8df7f80ad


Immutability issues with unions ring a bell for me. This may be related to 

mentions std.date.SysTime.

Here's a reduced version of your test case:
---
struct Rebindable
{
    union
    {
        int m;
        immutable int i;
    }
    void opAssign(Rebindable another) {}
}

struct Foo3
{
    // Remove the union or _timezone and dmd accepts it.
    union
    {
        int m;
        immutable int i;
    }
    Rebindable _timezone;
}

void main()
{
    Foo3 foo3;
    foo3 = Foo3();
}
---

[1] https://issues.dlang.org/show_bug.cgi?id=12885
[2] https://github.com/D-Programming-Language/dmd/pull/2665
Oct 15 2014