template cannot use local as parameter to non-global template

[Timon Gehr]

On 03/17/2013 05:36 PM, simendsjo wrote:
> On Sunday, 17 March 2013 at 16:21:25 UTC, Timon Gehr wrote:
>> On 03/17/2013 05:15 PM, simendsjo wrote:
>>> On Sunday, 17 March 2013 at 15:45:54 UTC, Timon Gehr wrote:
>>>> On 03/17/2013 01:54 PM, simendsjo wrote:
>>>>> I get a lot of these errors, and they can be quite tricky to get
>>>>> around
>>>>> and hurts my API.. Is this a temporary restriction in DMD, or is it
>>>>> another reason why this doesn't work?
>>>>>
>>>>> Error: template instance template!local cannot use local 'local' as
>>>>> parameter to non-global template innerTemplate(alias T)
>>>>
>>>> http://d.puremagic.com/issues/show_bug.cgi?id=5710
>>>
>>> Looks like the same issue. For me the use-case was a bit different
>>> though..
>>> I want to access struct members at CT only to look for UDAs, it's
>>> type etc.
>>> It works with workarounds, but the code gets ugly, and much convenience
>>> is lost..
>>>
>>> Too bad it looks like a wont-fix.
>>
>> It is not a wont-fix, and it actually should work.
>
> All the talk there looks to be around delegates. Would the same fix work
> for my struct members?

Of course. It is exactly the same issue. In D, if any kind of local 
symbol is passed to a templated function, the templated function 
requires a context pointer to access the local symbol. Non-static member 
functions require a 'this' reference.

Only one additional implicit pointer can be passed to a non-static 
member function at a time, since every member function must be able to 
provide delegates. Therefore, there must be an additional indirection 
somewhere. (Eg. pass the 'this' pointer as a local variable inside the 
delegate context.)