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digitalmars.D - Access template parameters at runtime

reply "Henning Pohl" <henning still-hidden.de> writes:
A struct is meant to take only integers as parameters:

struct SomeStruct(intergers...) {
     int opIndex(size_t idx) /* ... */ {
         return integers[idx]; // Error ...
     }
}

alias SomeStruct!(1, 2, 3) ss;


But it results in:
Error: undefined identifier integers, did you mean tuple 
intergers?


How can this problem be solved?
Aug 10 2012
next sibling parent reply Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
On 8/10/12 9:55 AM, Henning Pohl wrote:

 A struct is meant to take only integers as parameters:

 struct SomeStruct(intergers...) {
 int opIndex(size_t idx) /* ... */ {
 return integers[idx]; // Error ...
 }
 }

 alias SomeStruct!(1, 2, 3) ss;


 But it results in:
 Error: undefined identifier integers, did you mean tuple intergers?


 How can this problem be solved?



By fixing the typo?

Andrei
Aug 10 2012
parent reply travert phare.normalesup.org (Christophe Travert) writes:
"Henning Pohl" , dans le message (digitalmars.D:174569), a écrit :

 On Friday, 10 August 2012 at 14:10:38 UTC, Vladimir Panteleev 
 wrote:

 On Friday, 10 August 2012 at 14:10:02 UTC, Vladimir Panteleev
 wrote:

 On Friday, 10 August 2012 at 14:05:16 UTC, Henning Pohl wrote:

 Oups, sorry, imagine there isn't one.

 So the error is: variable idx cannot be read at compile time.



 You can't index a tuple during compilation.



 Sorry, meant to say - during runtime.



 Thats it, thank you :]



Note that if your design makes that you must have a tuple, you may build 
the array at compile time, so that you can index it at run time.
Aug 10 2012
next sibling parent travert phare.normalesup.org (Christophe Travert) writes:
"Henning Pohl" , dans le message (digitalmars.D:174572), a écrit :

 That is what I was trying first, but I could not make it work. 
 Maybe you can show me how it's done?



For example:

import std.stdio;

template TupleToArray(T...)
{
  static if (T.length == 1)
  {
    enum TupleToArray = [T[0]];
  }
  else
  {
    enum TupleToArray = TupleToArray!(T[0..$-1]) ~ T[$-1];
  }
}

void main()
{
  alias TupleToArray!(1, 2, 3) oneTwoThree;
  foreach (i; 0..3)
    writeln(oneTwoThree[i]);
}

output:
1
2
3

TupleToArray should have proper check to make clean code.
There must be something like that somewhere in phobos, or it should be 
added.

-- 
Christophe
Aug 10 2012
prev sibling next sibling parent Denis Shelomovskij <verylonglogin.reg gmail.com> writes:
10.08.2012 19:26, David Nadlinger пишет:

 Just use the compiler tuple inside an array literal, like this:
 [integers]. It will auto-expand, just when passing it to a method.



And if it's impossible/undesirable to create an array, you can do this:
---
foreach(i, t; your_tuple)
     if(i == idx)
         return t; // or do something else
assert(0);
---

-- 
Денис В. Шеломовский
Denis V. Shelomovskij
Aug 10 2012
prev sibling parent reply Dmitry Olshansky <dmitry.olsh gmail.com> writes:
On 11-Aug-12 00:58, Andrej Mitrovic wrote:

 On 8/10/12, jerro <a a.com> wrote:

 This would be one way to do it:




 On 8/10/12, Christophe Travert <travert phare.normalesup.org> wrote:

 For example:



 Guys I think you're overcomplecating it, you can just do:

 struct SomeStruct(integers...)
 {
      enum ints = [integers];
      int opIndex(size_t idx) /* ... */
      {
          return ints[idx];
      }
 }

 enum or static both work.



Internally identical to:

int opIndex(size_t idx)
{
	return [integers][idx];
}

Allocates on every call or not? I've no idea maybe Kenji fixed this already.


-- 
Dmitry Olshansky
Aug 10 2012
parent Timon Gehr <timon.gehr gmx.ch> writes:
On 08/10/2012 11:09 PM, Dmitry Olshansky wrote:

 On 11-Aug-12 00:58, Andrej Mitrovic wrote:

 On 8/10/12, jerro <a a.com> wrote:

 This would be one way to do it:




 On 8/10/12, Christophe Travert <travert phare.normalesup.org> wrote:

 For example:



 Guys I think you're overcomplecating it, you can just do:

 struct SomeStruct(integers...)
 {
      enum ints = [integers];
      int opIndex(size_t idx) /* ... */
      {
          return ints[idx];
      }
 }

 enum or static both work.



 Internally identical to:

 int opIndex(size_t idx)
 {
      return [integers][idx];
 }

 Allocates on every call or not? I've no idea maybe Kenji fixed this
 already.


 --
 Dmitry Olshansky



Still allocates in 2.060. static is the keyword of choice.
Aug 10 2012
prev sibling next sibling parent "Henning Pohl" <henning still-hidden.de> writes:
On Friday, 10 August 2012 at 14:02:08 UTC, Andrei Alexandrescu 
wrote:

 On 8/10/12 9:55 AM, Henning Pohl wrote:

 A struct is meant to take only integers as parameters:

 struct SomeStruct(intergers...) {
 int opIndex(size_t idx) /* ... */ {
 return integers[idx]; // Error ...
 }
 }

 alias SomeStruct!(1, 2, 3) ss;


 But it results in:
 Error: undefined identifier integers, did you mean tuple 
 intergers?


 How can this problem be solved?



 By fixing the typo?

 Andrei



Oups, sorry, imagine there isn't one.

So the error is: variable idx cannot be read at compile time.
Aug 10 2012
prev sibling next sibling parent "Vladimir Panteleev" <vladimir thecybershadow.net> writes:
On Friday, 10 August 2012 at 14:05:16 UTC, Henning Pohl wrote:

 Oups, sorry, imagine there isn't one.

 So the error is: variable idx cannot be read at compile time.



You can't index a tuple during compilation. You need to use an 
array:

struct SomeStruct(alias integers) {
     int opIndex(size_t idx) {
         return integers[idx];
     }
}

alias SomeStruct!([1, 2, 3]) ss;
Aug 10 2012
prev sibling next sibling parent "Vladimir Panteleev" <vladimir thecybershadow.net> writes:
On Friday, 10 August 2012 at 14:10:02 UTC, Vladimir Panteleev
wrote:

 On Friday, 10 August 2012 at 14:05:16 UTC, Henning Pohl wrote:

 Oups, sorry, imagine there isn't one.

 So the error is: variable idx cannot be read at compile time.



 You can't index a tuple during compilation.



Sorry, meant to say - during runtime.
Aug 10 2012
prev sibling next sibling parent "Henning Pohl" <henning still-hidden.de> writes:
On Friday, 10 August 2012 at 14:10:38 UTC, Vladimir Panteleev 
wrote:

 On Friday, 10 August 2012 at 14:10:02 UTC, Vladimir Panteleev
 wrote:

 On Friday, 10 August 2012 at 14:05:16 UTC, Henning Pohl wrote:

 Oups, sorry, imagine there isn't one.

 So the error is: variable idx cannot be read at compile time.



 You can't index a tuple during compilation.



 Sorry, meant to say - during runtime.



Thats it, thank you :]
Aug 10 2012
prev sibling next sibling parent "Henning Pohl" <henning still-hidden.de> writes:
On Friday, 10 August 2012 at 14:35:29 UTC, 
travert phare.normalesup.org (Christophe Travert) wrote:

 "Henning Pohl" , dans le message (digitalmars.D:174569), a 
 écrit :

 On Friday, 10 August 2012 at 14:10:38 UTC, Vladimir Panteleev 
 wrote:

 On Friday, 10 August 2012 at 14:10:02 UTC, Vladimir Panteleev
 wrote:

 On Friday, 10 August 2012 at 14:05:16 UTC, Henning Pohl 
 wrote:

 Oups, sorry, imagine there isn't one.

 So the error is: variable idx cannot be read at compile 
 time.



 You can't index a tuple during compilation.



 Sorry, meant to say - during runtime.



 Thats it, thank you :]



 Note that if your design makes that you must have a tuple, you 
 may build
 the array at compile time, so that you can index it at run time.



That is what I was trying first, but I could not make it work. 
Maybe you can show me how it's done?
Aug 10 2012
prev sibling next sibling parent "David Nadlinger" <see klickverbot.at> writes:
On Friday, 10 August 2012 at 14:42:24 UTC, Henning Pohl wrote:

 That is what I was trying first, but I could not make it work. 
 Maybe you can show me how it's done?



Just use the compiler tuple inside an array literal, like this: 
[integers]. It will auto-expand, just when passing it to a method.

David
Aug 10 2012
prev sibling next sibling parent "jerro" <a a.com> writes:
 Note that if your design makes that you must have a tuple, you 
 may build
 the array at compile time, so that you can index it at run 
 time.



 That is what I was trying first, but I could not make it work. 
 Maybe you can show me how it's done?



This would be one way to do it:


auto staticArray(Elements...)(Elements elements)
{
     alias Elements[0] E;
     E[Elements.length] r;

     foreach(i, _; elements)
         r[i] = elements[i];

     return r;
}

struct SomeStruct(integers...) {
     enum arr = staticArray(integers);
     int opIndex(size_t idx){
         return arr[idx];
     }
}
Aug 10 2012
prev sibling next sibling parent "David Nadlinger" <see klickverbot.at> writes:
On Friday, 10 August 2012 at 15:26:51 UTC, David Nadlinger wrote:

 It will auto-expand, just when passing it to a method.



Darn, that should have been: »just like when …«

David
Aug 10 2012
prev sibling next sibling parent "Henning Pohl" <henning still-hidden.de> writes:
Great, thank you :]

The solution provided by David seems to be shortest. You can even 
pass the ints directly.
Aug 10 2012
prev sibling next sibling parent Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
On 8/10/12, jerro <a a.com> wrote:

 This would be one way to do it:




On 8/10/12, Christophe Travert <travert phare.normalesup.org> wrote:

 For example:



Guys I think you're overcomplecating it, you can just do:

struct SomeStruct(integers...)
{
    enum ints = [integers];
    int opIndex(size_t idx) /* ... */
    {
        return ints[idx];
    }
}

enum or static both work.
Aug 10 2012
prev sibling parent Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
On 8/10/12, Dmitry Olshansky <dmitry.olsh gmail.com> wrote:

 Internally identical to:

 int opIndex(size_t idx)
 {
 	return [integers][idx];
 }

 Allocates on every call or not? I've no idea maybe Kenji fixed this
 already.



t's easy to check, add "writeln(&ints[idx]);" in opIndex and index [0]
several times. If the addresses change it means it allocates. It does
allocate every time when it's an enum but not if it's static.
Aug 10 2012