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digitalmars.D.learn - [D2] const vs structs

reply Richard Webb <webby beardmouse.org.uk> writes:
I just tried to build the Juno library with DMD 2.037, and got a bunch or
errors like:

juno\com\core.d(295): Error: function juno.com.core.GUID.opEquals type
signature should be const bool(ref const(GUID)) not bool(GUID other)

Which can be replicated with:
////////////////////////////////
struct Foo
{
	bool opEquals(Foo f) const
	{
		return true;
	}
}

void Bar()
{
	Foo f;
}
////////////////////////////////

It built ok with DMD2 a few months ago. Is this an intentional change?

Also, while looking at the problem i noticed that code like:

////////////////////////////////
struct Foo
{
	~this()
	{
		
	}
}

void Bar()
{
	const Foo f;
}
////////////////////////////////

Produces the error:

Error: destructor Foo.~this () is not callable using argument types ()

which seems a bit wrong?

Thanks,
Richard Webb
Dec 10 2009
parent reply "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Thu, 10 Dec 2009 19:23:43 -0500, Richard Webb <webby beardmouse.org.uk>  
wrote:


 I just tried to build the Juno library with DMD 2.037, and got a bunch  
 or errors like:

 juno\com\core.d(295): Error: function juno.com.core.GUID.opEquals type  
 signature should be const bool(ref const(GUID)) not bool(GUID other)

 Which can be replicated with:
 ////////////////////////////////
 struct Foo
 {
 	bool opEquals(Foo f) const
 	{
 		return true;
 	}
 }

 void Bar()
 {
 	Foo f;
 }
 ////////////////////////////////

 It built ok with DMD2 a few months ago. Is this an intentional change?


It's due to this change: http://www.dsource.org/projects/dmd/changeset/260

The issue being fixed was this:

http://d.puremagic.com/issues/show_bug.cgi?id=3433

I think it should be a bug, because your opEquals does not violate const,  
since you are making a copy of a Foo, and Foo contains no references.   
Please file a bug and reference 3433 and changeset 260.  I think it should  
be allowed to have a signature like this:

bool opEquals(T other) const

inside T as long as T can be implicitly cast from const to mutable.


 Also, while looking at the problem i noticed that code like:

 ////////////////////////////////
 struct Foo
 {
 	~this()
 	{
 		
 	}
 }

 void Bar()
 {
 	const Foo f;
 }
 ////////////////////////////////

 Produces the error:

 Error: destructor Foo.~this () is not callable using argument types ()

 which seems a bit wrong?


Yeah, that's weird.  Probably something to do with const.  Probably should  
file another bug :)

-Steve
Dec 11 2009
next sibling parent "Steven Schveighoffer" <schveiguy yahoo.com> writes:
On Fri, 11 Dec 2009 07:13:35 -0500, Steven Schveighoffer  
<schveiguy yahoo.com> wrote:



 I think it should be a bug


Clarifying, I meant it is a bug in the compiler *not* in Juno :)

-Steve
Dec 11 2009
prev sibling parent Richard Webb <webby beardmouse.org.uk> writes:
Opened as 3606 and 3607.

Thanks,
Richard Webb
Dec 11 2009