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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
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 "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
parent reply "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
parent reply "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
parent reply "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
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
parent reply "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
next sibling parent reply "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
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 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 next sibling parent reply "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
parent reply 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
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
next 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
prev sibling 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 parent reply 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
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