struct SomeStruct {
	string p;
	string q;
	string[] pq;
}

ErrorMessage[] pq;
session.set("registerBody", pq);

/home/venkat/.dub/packages/vibe-d-0.8.4/vibe-d/http/vibe/http/session.d(83,3): Error: static assert:  "Type SomeStruct contains references, which is not supported for session storage."


vibe.d session won't let me put in a simple struct with an array or an associative array. session.put calls std.traits.hasAliasing which is returning true when I have either an array or an associative array. I looked through the std.traits.hasAliasing code. I can't make a whole lot of sense there.

The hasAliasing function documentation says as long as the array or associative array are not immutable it should return true. Since session.put does !hasAliasing I changed string[] to immutable, that throws a whole lot of other compilation error messages.

What is hasAliasing doing ?

On Sunday, 29 July 2018 at 01:05:19 UTC, Venkat wrote:
> struct SomeStruct {
> 	string p;
> 	string q;
> 	string[] pq;
> }
>
Session session = req.session;
session.get!SomeStruct("registerBody");
>
> /home/venkat/.dub/packages/vibe-d-0.8.4/vibe-d/http/vibe/http/session.d(83,3): Error: static assert:  "Type SomeStruct contains references, which is not supported for session storage."
>
>
> vibe.d session won't let me put in a simple struct with an array or an associative array. session.put calls std.traits.hasAliasing which is returning true when I have either an array or an associative array. I looked through the std.traits.hasAliasing code. I can't make a whole lot of sense there.
>
> The hasAliasing function documentation says as long as the array or associative array are not immutable it should return true. Since session.put does !hasAliasing I changed string[] to immutable, that throws a whole lot of other compilation error messages.
>
> What is hasAliasing doing ?

Posted the wrong code. Fixed it above. Reposting below for clarity. For the record both session.get and session.put call hasAliasing.

struct SomeStruct {
	string p;
	string q;
	string[] pq;
}

Session session = req.session;
session.get!SomeStruct("registerBody");

On 7/28/18 9:21 PM, Venkat wrote:
> On Sunday, 29 July 2018 at 01:05:19 UTC, Venkat wrote:
>> struct SomeStruct {
>>     string p;
>>     string q;
>>     string[] pq;
>> }
>>
> Session session = req.session;
> session.get!SomeStruct("registerBody");
>>
>> /home/venkat/.dub/packages/vibe-d-0.8.4/vibe-d/http/vibe/http/session.d(83,3): Error: static assert:  "Type SomeStruct contains references, which is not supported for session storage."

What is happening is the session storage is complaining it can't store the array. I think because the array data could change without the struct itself changing.

Even though string has a pointer, the data is immutable, so it is allowed.

>>
>>
>> vibe.d session won't let me put in a simple struct with an array or an associative array. session.put calls std.traits.hasAliasing which is returning true when I have either an array or an associative array. I looked through the std.traits.hasAliasing code. I can't make a whole lot of sense there.
>>
>> The hasAliasing function documentation says as long as the array or associative array are not immutable it should return true. Since session.put does !hasAliasing I changed string[] to immutable, that throws a whole lot of other compilation error messages.
>>
>> What is hasAliasing doing ?

hasAliasing means there are references to mutable data somewhere in your struct. In this case, the array pq is a reference to mutable data (yes, the strings inside are immutable, but they can be changed).

The qualifications are listed here:
https://dlang.org/library/std/traits/has_aliasing.html

"an array U[] and U is not immutable"

Try immutable(string)[] pq.

-Steve

Thankyou.