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Access template parameters at runtime
Aug 10, 2012
Henning Pohl
Aug 10, 2012
Henning Pohl
Aug 10, 2012
Vladimir Panteleev
Aug 10, 2012
Vladimir Panteleev
Aug 10, 2012
Henning Pohl
Aug 10, 2012
Christophe Travert
Aug 10, 2012
Henning Pohl
Aug 10, 2012
David Nadlinger
Aug 10, 2012
David Nadlinger
Aug 10, 2012
Denis Shelomovskij
Aug 10, 2012
jerro
Aug 10, 2012
Andrej Mitrovic
Aug 10, 2012
Dmitry Olshansky
Aug 10, 2012
Andrej Mitrovic
Aug 10, 2012
Timon Gehr
Aug 10, 2012
Christophe Travert
Aug 10, 2012
Henning Pohl
```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?

```
```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

```
```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.
```
```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;

```
```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.
```
```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 :]
```
```"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.
```
```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?
```
```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
```
```>> 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];
}
}

```
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