I have the following code which is massively simplified from a larger type. The problem occurs between assigning the value to the type and retrieving it.

The value is assigned through opAssign and the assert passes. When using a property to retrieve the same data the assert fails!

import std.bitmanip;
import std.stdio;
import std.traits;

struct IpAddress
{
	private ubyte[] _octets;

	this(uint value)
	{
		this.opAssign(value);
	}

	public @property ubyte[] data()
	{
		assert(this._octets == [1, 2, 3, 4]);
		return this._octets;
	}

	public void opAssign(uint value)
	{
		this._octets = value.nativeToBigEndian();
		assert(this._octets == [1, 2, 3, 4]);
	}
}

unittest
{
	auto ipAddress = IpAddress(0x01020304);
	assert(ipAddress.data == [1, 2, 3, 4]);
}

Any ideas why?

On a side note i also expected nativeToBigEndian to byte flip the hex literal, no idea why it hasn't, it's been a long day... I'm using MacOSX (Intel).

Compiled with: rdmd --force -de -debug -main -property -unittest -w file.d

On Friday, 13 December 2013 at 16:37:51 UTC, Gary Willoughby wrote:
> I have the following code which is massively simplified from a larger type. The problem occurs between assigning the value to the type and retrieving it.
>
> The value is assigned through opAssign and the assert passes. When using a property to retrieve the same data the assert fails!
>
> import std.bitmanip;
> import std.stdio;
> import std.traits;
>
> struct IpAddress
> {
> 	private ubyte[] _octets;
>
> 	this(uint value)
> 	{
> 		this.opAssign(value);
> 	}
>
> 	public @property ubyte[] data()
> 	{
> 		assert(this._octets == [1, 2, 3, 4]);
> 		return this._octets;
> 	}
>
> 	public void opAssign(uint value)
> 	{
> 		this._octets = value.nativeToBigEndian();
> 		assert(this._octets == [1, 2, 3, 4]);
> 	}
> }
>
> unittest
> {
> 	auto ipAddress = IpAddress(0x01020304);
> 	assert(ipAddress.data == [1, 2, 3, 4]);
> }
>
> Any ideas why?
>
> On a side note i also expected nativeToBigEndian to byte flip the hex literal, no idea why it hasn't, it's been a long day... I'm using MacOSX (Intel).
>
> Compiled with: rdmd --force -de -debug -main -property -unittest -w file.d

opAssign is escaping a reference to its stack by assigning the static array to the slice _octets. Therefore, garbage.

It works fine when using dup to the value returned by nativeToBigEndian:
    public void opAssign(uint value)
    {
        this._octets = value.nativeToBigEndian().dup;
        assert(this._octets == cast (ubyte[]) [1, 2, 3, 4]);
    }



On 12/13/2013 06:35 PM, John Colvin wrote:
> On Friday, 13 December 2013 at 16:37:51 UTC, Gary Willoughby wrote:
>> I have the following code which is massively simplified from a larger
>> type. The problem occurs between assigning the value to the type and
>> retrieving it.
>>
>> The value is assigned through opAssign and the assert passes. When
>> using a property to retrieve the same data the assert fails!
>>
>> import std.bitmanip;
>> import std.stdio;
>> import std.traits;
>>
>> struct IpAddress
>> {
>>     private ubyte[] _octets;
>>
>>     this(uint value)
>>     {
>>         this.opAssign(value);
>>     }
>>
>>     public @property ubyte[] data()
>>     {
>>         assert(this._octets == [1, 2, 3, 4]);
>>         return this._octets;
>>     }
>>
>>     public void opAssign(uint value)
>>     {
>>         this._octets = value.nativeToBigEndian();
>>         assert(this._octets == [1, 2, 3, 4]);
>>     }
>> }
>>
>> unittest
>> {
>>     auto ipAddress = IpAddress(0x01020304);
>>     assert(ipAddress.data == [1, 2, 3, 4]);
>> }
>>
>> Any ideas why?
>>
>> On a side note i also expected nativeToBigEndian to byte flip the hex
>> literal, no idea why it hasn't, it's been a long day... I'm using
>> MacOSX (Intel).
>>
>> Compiled with: rdmd --force -de -debug -main -property -unittest -w
>> file.d
>
> opAssign is escaping a reference to its stack by assigning the static
> array to the slice _octets. Therefore, garbage.

On Friday, 13 December 2013 at 18:01:53 UTC, Rémy Mouëza wrote:
>
> It works fine when using dup to the value returned by nativeToBigEndian:
>     public void opAssign(uint value)
>     {
>         this._octets = value.nativeToBigEndian().dup;
>         assert(this._octets == cast (ubyte[]) [1, 2, 3, 4]);
>     }
>

As expected, as dup allocates a new array on the heap.

On Friday, 13 December 2013 at 17:35:27 UTC, John Colvin wrote:
> On Friday, 13 December 2013 at 16:37:51 UTC, Gary Willoughby wrote:
>> I have the following code which is massively simplified from a larger type. The problem occurs between assigning the value to the type and retrieving it.
>>
>> The value is assigned through opAssign and the assert passes. When using a property to retrieve the same data the assert fails!
>>
>> import std.bitmanip;
>> import std.stdio;
>> import std.traits;
>>
>> struct IpAddress
>> {
>> 	private ubyte[] _octets;
>>
>> 	this(uint value)
>> 	{
>> 		this.opAssign(value);
>> 	}
>>
>> 	public @property ubyte[] data()
>> 	{
>> 		assert(this._octets == [1, 2, 3, 4]);
>> 		return this._octets;
>> 	}
>>
>> 	public void opAssign(uint value)
>> 	{
>> 		this._octets = value.nativeToBigEndian();
>> 		assert(this._octets == [1, 2, 3, 4]);
>> 	}
>> }
>>
>> unittest
>> {
>> 	auto ipAddress = IpAddress(0x01020304);
>> 	assert(ipAddress.data == [1, 2, 3, 4]);
>> }
>>
>> Any ideas why?
>>
>> On a side note i also expected nativeToBigEndian to byte flip the hex literal, no idea why it hasn't, it's been a long day... I'm using MacOSX (Intel).
>>
>> Compiled with: rdmd --force -de -debug -main -property -unittest -w file.d
>
> opAssign is escaping a reference to its stack by assigning the static array to the slice _octets. Therefore, garbage.

I'm not going to lie that has gone over my head a little. Could you explain it more simply please? I just want to totally understand the issue here. Thanks.

On 12/14/2013 10:48 AM, Gary Willoughby wrote:

> On Friday, 13 December 2013 at 17:35:27 UTC, John Colvin wrote:

>>>     public void opAssign(uint value)
>>>     {
>>>         this._octets = value.nativeToBigEndian();
>>>         assert(this._octets == [1, 2, 3, 4]);
>>>     }
>>> }

>> opAssign is escaping a reference to its stack by assigning the static
>> array to the slice _octets. Therefore, garbage.
>
> I'm not going to lie that has gone over my head a little. Could you
> explain it more simply please? I just want to totally understand the
> issue here. Thanks.

According to documentation, nativeToBigEndian returns a static array (fixed-length array):

  http://dlang.org/phobos/std_bitmanip.html#.nativeToBigEndian

It says "returns it as a ubyte[n] where n is the size of the given type."

Since static arrays normally live on the stack, the returned array is a local array.

As with any slice assignment, the assignment to this._octets in opAssign makes _octets a slice to the elements of that local array. Upon leaving opAssign that array is no more. So, _octets is left referring to elements that are long gone. :(

Ali

On Sunday, 15 December 2013 at 00:21:37 UTC, Ali Çehreli wrote:
> On 12/14/2013 10:48 AM, Gary Willoughby wrote:
>
> > On Friday, 13 December 2013 at 17:35:27 UTC, John Colvin
> wrote:
>
> >>>     public void opAssign(uint value)
> >>>     {
> >>>         this._octets = value.nativeToBigEndian();
> >>>         assert(this._octets == [1, 2, 3, 4]);
> >>>     }
> >>> }
>
> >> opAssign is escaping a reference to its stack by assigning
> the static
> >> array to the slice _octets. Therefore, garbage.
> >
> > I'm not going to lie that has gone over my head a little.
> Could you
> > explain it more simply please? I just want to totally
> understand the
> > issue here. Thanks.
>
> According to documentation, nativeToBigEndian returns a static array (fixed-length array):
>
>   http://dlang.org/phobos/std_bitmanip.html#.nativeToBigEndian
>
> It says "returns it as a ubyte[n] where n is the size of the given type."
>
> Since static arrays normally live on the stack, the returned array is a local array.
>
> As with any slice assignment, the assignment to this._octets in opAssign makes _octets a slice to the elements of that local array. Upon leaving opAssign that array is no more. So, _octets is left referring to elements that are long gone. :(
>
> Ali

Ah right, that now makes perfect sense. Thanks all! :)