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digitalmars.D.learn - use template function without assignment

reply "JS" <js.mdnq gmail.com> writes:
I have created a template Pragma that emulates pragma but better, 
the problem is that I have to assign it to something which is 
very redundant in my code:

enum temp = Pragma!(msg)

e.g.,

template Pragma(alias amsg)
{
     string Pragma(string file = __FILE__)
     {
         pragma(msg, amsg);
         return "";
     }
}

When I try to use void instead of string and do something like

Pragma!(msg)

I get an error that the template has no effect. It does have an 
effect but what it is complaining about is exactly what I want.

I've tried all kinds of combinations(mixins work but I then can't 
ise __FILE__) and nothing works. Maybe someone has an idea.
Jul 29 2013
next sibling parent reply "Meta" <jared771 gmail.com> writes:
On Monday, 29 July 2013 at 23:09:20 UTC, JS wrote:

 I have created a template Pragma that emulates pragma but 
 better, the problem is that I have to assign it to something 
 which is very redundant in my code:

 enum temp = Pragma!(msg)

 e.g.,

 template Pragma(alias amsg)
 {
     string Pragma(string file = __FILE__)
     {
         pragma(msg, amsg);
         return "";
     }
 }

 When I try to use void instead of string and do something like

 Pragma!(msg)

 I get an error that the template has no effect. It does have an 
 effect but what it is complaining about is exactly what I want.

 I've tried all kinds of combinations(mixins work but I then 
 can't ise __FILE__) and nothing works. Maybe someone has an 
 idea.


Does this code do what you want, or are there other requirements 
as well?

void Pragma(alias amsg)(string file = __FILE__)
{
	pragma(msg, amsg);
}
Jul 29 2013
parent reply "Meta" <jared771 gmail.com> writes:
On Tuesday, 30 July 2013 at 01:06:39 UTC, Meta wrote:

 Does this code do what you want, or are there other 
 requirements as well?

 void Pragma(alias amsg)(string file = __FILE__)
 {
 	pragma(msg, amsg);
 }


Actually, sorry, that's the exact same code, just with some 
syntactic sugar. To avoid the "expression has no effect" problem, 
you could use an alias instead of an enum. You're getting the 
error when you try to use pragma in the "global" scope, right?

void Pragma(alias amsg)(string file = __FILE__)
{
     pragma(msg, amsg);
}

alias temp = Pragma!("test");

In general, D doesn't have top-level expressions like what I 
think you want to do here. Maybe somebody else knows a way to 
work around that.
Jul 29 2013
parent reply "JS" <js.mdnq gmail.com> writes:
On Tuesday, 30 July 2013 at 01:19:23 UTC, Meta wrote:

 On Tuesday, 30 July 2013 at 01:06:39 UTC, Meta wrote:

 Does this code do what you want, or are there other 
 requirements as well?

 void Pragma(alias amsg)(string file = __FILE__)
 {
 	pragma(msg, amsg);
 }


 Actually, sorry, that's the exact same code, just with some 
 syntactic sugar. To avoid the "expression has no effect" 
 problem, you could use an alias instead of an enum. You're 
 getting the error when you try to use pragma in the "global" 
 scope, right?

 void Pragma(alias amsg)(string file = __FILE__)
 {
     pragma(msg, amsg);
 }

 alias temp = Pragma!("test");

 In general, D doesn't have top-level expressions like what I 
 think you want to do here. Maybe somebody else knows a way to 
 work around that.


If I use enum or alias they both have the same problem(The 
annoying mandatory assignment).

I see the reason why it does it but I don't know it because in 
this case I do not want an effect. (pragma has no "effect" which 
is what I'm trying to emulate... works well except for that 
annoying quirk of having to assign it to something).

BTW, is

void Pragma(alias amsg)(string file = __FILE__)

short for

template Pragma(alias amsg)
{
  void Pragma(string file = __FILE__)

or is there some real difference?

I could potential do something like

template Group(alias G1)
{
     void Group(alias G2)(int s)
     {
         writeln(s);
     }
}

Group!("x")("y")(3); // doesn't work,
Group!("x")!("y")(3); // doesn't work
Jul 30 2013
parent reply "Meta" <jared771 gmail.com> writes:
On Tuesday, 30 July 2013 at 07:02:51 UTC, JS wrote:

 If I use enum or alias they both have the same problem(The 
 annoying mandatory assignment).


Can you post some more code that exhibits exactly the behaviour 
you're describing? I can't replicate the problem you're having 
with the code you provided (nor the code *I* provided).


 BTW, is

 void Pragma(alias amsg)(string file = __FILE__)

 short for

 template Pragma(alias amsg)
 {
  void Pragma(string file = __FILE__)

 or is there some real difference?


They're semantically equivalent. The first form is just shorthand 
for the second.


 I could potential do something like

 template Group(alias G1)
 {
     void Group(alias G2)(int s)
     {
         writeln(s);
     }
 }

 Group!("x")("y")(3); // doesn't work,
 Group!("x")!("y")(3); // doesn't work


What you're doing here is pretty weird. That code is equivalent 
to:

template Group(alias G1)
{
     template Group(alias G2)
     {
         void Group(int s)
         {
             writeln(s);
         }
     }
}

And I really have no idea how it *should* behave. It definitely 
doesn't work on dpaste.dzfl.pl.
Jul 30 2013
parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 07/30/2013 06:16 AM, Meta wrote:


 Can you post some more code that exhibits exactly the behaviour you're
 describing? I can't replicate the problem you're having with the code
 you provided (nor the code *I* provided).


Ditto.

JS, I wrote the following code for you. Could you please start with it 
and show us the problem that we are trying to solve.

template Pragma(alias amsg)
{
     void Pragma(string file = __FILE__)
     {
         pragma(msg, amsg);
     }
}

void main()
{
     enum msg = "hello";
     Pragma!msg;
}

Ali
Jul 30 2013
parent reply "JS" <js.mdnq gmail.com> writes:
On Tuesday, 30 July 2013 at 18:38:23 UTC, Ali Çehreli wrote:

 On 07/30/2013 06:16 AM, Meta wrote:


 Can you post some more code that exhibits exactly the


 behaviour you're

 describing? I can't replicate the problem you're having with


 the code

 you provided (nor the code *I* provided).


 Ditto.

 JS, I wrote the following code for you. Could you please start 
 with it and show us the problem that we are trying to solve.

 template Pragma(alias amsg)
 {
     void Pragma(string file = __FILE__)
     {
         pragma(msg, amsg);
     }
 }

 void main()
 {
     enum msg = "hello";
     Pragma!msg;
 }

 Ali


I already stated why this is not a proper example, I'm not using 
Pragma in run time code(for lack of a better term).

module main;

import std.stdio;


template Pragma(alias amsg)
{
     void Pragma(string file = __FILE__)
     {
         pragma(msg, amsg);
     }
}

template t()
{
     Pragma!("help, this does not work!!!!!!!!!");
}

void main()
{
     enum msg = "hello";
     Pragma!msg;
     t!();
}
Jul 30 2013
parent reply =?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:
On 07/30/2013 12:09 PM, JS wrote:


 I already stated why this is not a proper example, I'm not using Pragma
 in run time code(for lack of a better term).

 module main;

 import std.stdio;


 template Pragma(alias amsg)
 {
      void Pragma(string file = __FILE__)
      {
          pragma(msg, amsg);
      }
 }

 template t()
 {
      Pragma!("help, this does not work!!!!!!!!!");
 }

 void main()
 {
      enum msg = "hello";
      Pragma!msg;
      t!();
 }


Thank you. Now we have something to work on. The program above produces 
the following error:

Error: no identifier for declarator Pragma!"help, this does not 
work!!!!!!!!!"

The error is fixed by adding a mixin:

     mixin Pragma!("help, this does not work!!!!!!!!!");

Despite another error it actually works:

hello
help, this does not work!!!!!!!!!    <-- IT WORKED
Error: t!() has no effect

The second error is fixed by another mixin:

     mixin t!();

Perhaps the example is too simplistic. Still, let's stay with it for 
further issues.

Ali
Jul 30 2013
parent reply "JS" <js.mdnq gmail.com> writes:
On Tuesday, 30 July 2013 at 20:34:32 UTC, Ali Çehreli wrote:

 On 07/30/2013 12:09 PM, JS wrote:


 I already stated why this is not a proper example, I'm not


 using Pragma

 in run time code(for lack of a better term).

 module main;

 import std.stdio;


 template Pragma(alias amsg)
 {
      void Pragma(string file = __FILE__)
      {
          pragma(msg, amsg);
      }
 }

 template t()
 {
      Pragma!("help, this does not work!!!!!!!!!");
 }

 void main()
 {
      enum msg = "hello";
      Pragma!msg;
      t!();
 }


 Thank you. Now we have something to work on. The program above 
 produces the following error:

 Error: no identifier for declarator Pragma!"help, this does not 
 work!!!!!!!!!"

 The error is fixed by adding a mixin:

     mixin Pragma!("help, this does not work!!!!!!!!!");


Or just assigning it to enum... both are not great solutions...


 Despite another error it actually works:

 hello
 help, this does not work!!!!!!!!!    <-- IT WORKED
 Error: t!() has no effect

 The second error is fixed by another mixin:

     mixin t!();

 Perhaps the example is too simplistic. Still, let's stay with 
 it for further issues.

 Ali


I think that such behavior should not be an error but possibly a 
warning, if at all.

And if you cared to read what I initially posted you would 
realize I already explained the same thing. The example maybe 
more clear but I stated, maybe in some convoluted and jumped way, 
that Pragma doesn't work *in* templates..

"When I try to use void instead of string and do something like

Pragma!(msg)

I get an error that the template has no effect."

and later

"It's goal is to debug templates and essentially
just wrapping pragma to supply the __FILE__ info automatically.

e.g., instead of having to do

pragma(msg, __FILE__~amsg);

I want to do Pragma!(amsg);
"
Jul 30 2013
parent "JS" <js.mdnq gmail.com> writes:
BTW, when I use mixin in my code, the error goes away but no 
pragma msg is produced, so it is not a solution.
Jul 30 2013
prev sibling parent reply "Namespace" <rswhite4 googlemail.com> writes:
On Monday, 29 July 2013 at 23:09:20 UTC, JS wrote:

 I have created a template Pragma that emulates pragma but 
 better, the problem is that I have to assign it to something 
 which is very redundant in my code:

 enum temp = Pragma!(msg)

 e.g.,

 template Pragma(alias amsg)
 {
     string Pragma(string file = __FILE__)
     {
         pragma(msg, amsg);
         return "";
     }
 }

 When I try to use void instead of string and do something like

 Pragma!(msg)

 I get an error that the template has no effect. It does have an 
 effect but what it is complaining about is exactly what I want.

 I've tried all kinds of combinations(mixins work but I then 
 can't ise __FILE__) and nothing works. Maybe someone has an 
 idea.


You could call your template in a static CTor:

----
import std.stdio;

template Pragma(alias amsg)
{
     void Pragma(string file = __FILE__)
     {
         pragma(msg, amsg);
     }
}

static this() {
	Pragma!("foo")();
}

void main()
{
	writeln("Hello world!");
}
----

Maybe this helps?
Jul 30 2013
parent "JS" <js.mdnq gmail.com> writes:
On Tuesday, 30 July 2013 at 07:12:11 UTC, Namespace wrote:

 On Monday, 29 July 2013 at 23:09:20 UTC, JS wrote:

 I have created a template Pragma that emulates pragma but 
 better, the problem is that I have to assign it to something 
 which is very redundant in my code:

 enum temp = Pragma!(msg)

 e.g.,

 template Pragma(alias amsg)
 {
    string Pragma(string file = __FILE__)
    {
        pragma(msg, amsg);
        return "";
    }
 }

 When I try to use void instead of string and do something like

 Pragma!(msg)

 I get an error that the template has no effect. It does have 
 an effect but what it is complaining about is exactly what I 
 want.

 I've tried all kinds of combinations(mixins work but I then 
 can't ise __FILE__) and nothing works. Maybe someone has an 
 idea.


 You could call your template in a static CTor:

 ----
 import std.stdio;

 template Pragma(alias amsg)
 {
     void Pragma(string file = __FILE__)
     {
         pragma(msg, amsg);
     }
 }

 static this() {
 	Pragma!("foo")();
 }

 void main()
 {
 	writeln("Hello world!");
 }
 ----

 Maybe this helps?


This is useless. It's goal is to debug templates and essentially 
just wrapping pragma to supply the __FILE__ info automatically.

e.g., instead of having to do

pragma(msg, __FILE__~amsg);

I want to do Pragma!(amsg);

where Pragma custom formats the error or info message with the 
location where the message was initiated.

Sticking it in a ctor will only print a message from that 
location.
Jul 30 2013