Hi,
There doesn't seem to be something like this in Phobos:

alias Instantiate(alias Template, T...) = Template!T;

Here's an example of why I need it:

alias staticEx(string msg, string file = __FILE__, size_t line = __LINE__) =
	Instantiate!(.staticEx!(Exception, msg), file, line);

template staticEx(T:Throwable, args...)
{
	auto staticEx(string file = __FILE__, size_t line = __LINE__)()
	...

Full code:
http://dpaste.dzfl.pl/810e55b1acd76

I found std.meta.ApplyLeft but it doesn't seem to work here. I've needed this before and ended up doing a workaround with a template block and temporary alias but it might be nice if Phobos had this. Or is there a simpler solution?

On 4/21/16 10:47 AM, Nick Treleaven wrote:
> Hi,
> There doesn't seem to be something like this in Phobos:
>
> alias Instantiate(alias Template, T...) = Template!T;
>
> Here's an example of why I need it:
>
> alias staticEx(string msg, string file = __FILE__, size_t line =
> __LINE__) =
>      Instantiate!(.staticEx!(Exception, msg), file, line);
>
> template staticEx(T:Throwable, args...)
> {
>      auto staticEx(string file = __FILE__, size_t line = __LINE__)()
>      ...
>
> Full code:
> http://dpaste.dzfl.pl/810e55b1acd76
>
> I found std.meta.ApplyLeft but it doesn't seem to work here. I've needed
> this before and ended up doing a workaround with a template block and
> temporary alias but it might be nice if Phobos had this. Or is there a
> simpler solution?

This doesn't work?

alias staticEx(string msg, string file = __FILE__, size_t line = __LINE__) = staticEx!(Exception, msg).staticEx!(file, line);

I would think something with AliasSeq could come in handy, it's the way to alias a compile-time list.

-Steve

On 21/04/2016 18:03, Steven Schveighoffer wrote:
> This doesn't work?
>
> alias staticEx(string msg, string file = __FILE__, size_t line =
> __LINE__) = staticEx!(Exception, msg).staticEx!(file, line);

No, nor using the module dot prefix `= .staticEx!(...).staticEx` either:

staticex.d(3): Error: template identifier 'staticEx' is not a member of template 'staticex.staticEx!(Exception, "Look ma, @nogc exception!").staticEx(string file = __FILE__, uint line = __LINE__)()'
staticex.d(20): Error: template instance staticex.staticEx!("Look ma, @nogc exception!", "staticex.d", 20u) error instantiating

> I would think something with AliasSeq could come in handy, it's the way
> to alias a compile-time list.

Not sure how that would help.

On 4/22/16 6:50 AM, Nick Treleaven wrote:
> On 21/04/2016 18:03, Steven Schveighoffer wrote:
>> This doesn't work?
>>
>> alias staticEx(string msg, string file = __FILE__, size_t line =
>> __LINE__) = staticEx!(Exception, msg).staticEx!(file, line);
>
> No, nor using the module dot prefix `= .staticEx!(...).staticEx` either:
>
> staticex.d(3): Error: template identifier 'staticEx' is not a member of
> template 'staticex.staticEx!(Exception, "Look ma, @nogc
> exception!").staticEx(string file = __FILE__, uint line = __LINE__)()'
> staticex.d(20): Error: template instance staticex.staticEx!("Look ma,
> @nogc exception!", "staticex.d", 20u) error instantiating

OK, I get it. I think this used to work, but I think D has long since disallowed direct access to eponymous members.

So what you really want to do is:

staticEx!(Exception, msg)!(file, line), but of course this doesn't follow proper grammar.

I think you are right, this cannot be done without such a template. It brings back access to the eponymous nested template, interesting. I think we should add it.

>> I would think something with AliasSeq could come in handy, it's the way
>> to alias a compile-time list.
>
> Not sure how that would help.

I didn't realize what the issue was.

-Steve

On 22/04/2016 14:40, Steven Schveighoffer wrote:
> OK, I get it. I think this used to work, but I think D has long since
> disallowed direct access to eponymous members.
>
> So what you really want to do is:
>
> staticEx!(Exception, msg)!(file, line), but of course this doesn't
> follow proper grammar.
>
> I think you are right, this cannot be done without such a template. It
> brings back access to the eponymous nested template, interesting. I
> think we should add it.

OK, great :-)

On Thursday, 21 April 2016 at 14:47:55 UTC, Nick Treleaven wrote:
> I found std.meta.ApplyLeft but it doesn't seem to work here. I've needed this before and ended up doing a workaround with a template block and temporary alias but it might be nice if Phobos had this. Or is there a simpler solution?

From std.meta:

---
/*
 * Instantiates the given template with the given list of parameters.
 *
 * Used to work around syntactic limitations of D with regard to instantiating
 * a template from an alias sequence (e.g. T[0]!(...) is not valid) or a template
 * returning another template (e.g. Foo!(Bar)!(Baz) is not allowed).
 */
// TODO: Consider publicly exposing this, maybe even if only for better
// understandability of error messages.
alias Instantiate(alias Template, Params...) = Template!Params;
---

;)

 — David

On Friday, 22 April 2016 at 19:09:40 UTC, David Nadlinger wrote:
> From std.meta:
>
> ---
> /*
>  * Instantiates the given template with the given list of parameters.
>  *
>  * Used to work around syntactic limitations of D with regard to instantiating
>  * a template from an alias sequence (e.g. T[0]!(...) is not valid) or a template
>  * returning another template (e.g. Foo!(Bar)!(Baz) is not allowed).
>  */
> // TODO: Consider publicly exposing this, maybe even if only for better
> // understandability of error messages.
> alias Instantiate(alias Template, Params...) = Template!Params;

Ah, maybe I'd even seen this in passing and forgot. Good point about aliasSeq template elements, let's make this public.

On 25/04/2016 11:16, Nick Treleaven wrote:
> On Friday, 22 April 2016 at 19:09:40 UTC, David Nadlinger wrote:
>> alias Instantiate(alias Template, Params...) = Template!Params;
>
> Ah, maybe I'd even seen this in passing and forgot. Good point about
> aliasSeq template elements, let's make this public.

https://github.com/dlang/phobos/pull/4234