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digitalmars.D.learn - Instantiate!(Template, args) in Phobos?

reply Nick Treleaven <ntrel-pub mybtinternet.com> writes:
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?
Apr 21 2016
next sibling parent reply Steven Schveighoffer <schveiguy yahoo.com> writes:
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
Apr 21 2016
parent reply Nick Treleaven <ntrel-pub mybtinternet.com> writes:
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.
Apr 22 2016
parent reply Steven Schveighoffer <schveiguy yahoo.com> writes:
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
Apr 22 2016
parent Nick Treleaven <ntrel-pub mybtinternet.com> writes:
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 :-)
Apr 22 2016
prev sibling parent reply David Nadlinger <code klickverbot.at> writes:
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
Apr 22 2016
parent reply Nick Treleaven <ntrel-pub mybtinternet.com> writes:
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.
Apr 25 2016
parent Nick Treleaven <ntrel-pub mybtinternet.com> writes:
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
Apr 25 2016