• Dark Hole (25/25) Feb 22 2023 I'm trying to rewrite really old D code. There was fragment like
• Paul Backus (6/20) Feb 22 2023 Pretty sure this is just a bug. There are a lot of edge-case bugs
• Elfstone (18/44) Feb 23 2023 I never used really old D compiler, but the error looks

Dark Hole <dark.hole1 yandex.ru> writes:

I'm trying to rewrite really old D code. There was fragment like 
that:
```d
template Foo(T, T[] Array) {
     // ...
}
// ...
Bar[] arr;
Foo!(Bar, arr);
```

This gives error `can't read arr in compile time`. Small changes:
```d
template Foo(T, alias T[] Array) {
     // ...
}
// ...
Bar[] arr;
Foo!(Bar, arr);
```

This is valid D, but it doesn't work. It gives error "Error: 
template instance `Foo!(Bar, arr)` does not match template 
declaration `Foo(T, alias T[] Array)`".

Of course, there is some ways to avoid this error (e.g. check 
Array type in if), but I don't undestand why this code doesn't 
compiles.

Paul Backus <snarwin gmail.com> writes:

On Wednesday, 22 February 2023 at 20:20:46 UTC, Dark Hole wrote:
 ```d
 template Foo(T, alias T[] Array) {
     // ...
 }
 // ...
 Bar[] arr;
 Foo!(Bar, arr);
 ```

 This is valid D, but it doesn't work. It gives error "Error: 
 template instance `Foo!(Bar, arr)` does not match template 
 declaration `Foo(T, alias T[] Array)`".

 Of course, there is some ways to avoid this error (e.g. check 
 Array type in if), but I don't undestand why this code doesn't 
 compiles.

Pretty sure this is just a bug. There are a lot of edge-case bugs 
like this where template instantiation doesn't work the way it's 
supposed to.

I've submitted a bug report for this on issues.dlang.org: 
https://issues.dlang.org/show_bug.cgi?id=23733

Elfstone <elfstone yeah.net> writes:

On Wednesday, 22 February 2023 at 20:20:46 UTC, Dark Hole wrote:
 I'm trying to rewrite really old D code. There was fragment 
 like that:
 ```d
 template Foo(T, T[] Array) {
     // ...
 }
 // ...
 Bar[] arr;
 Foo!(Bar, arr);
 ```

 This gives error `can't read arr in compile time`. Small 
 changes:
 ```d
 template Foo(T, alias T[] Array) {
     // ...
 }
 // ...
 Bar[] arr;
 Foo!(Bar, arr);
 ```

 This is valid D, but it doesn't work. It gives error "Error: 
 template instance `Foo!(Bar, arr)` does not match template 
 declaration `Foo(T, alias T[] Array)`".

 Of course, there is some ways to avoid this error (e.g. check 
 Array type in if), but I don't undestand why this code doesn't 
 compiles.

I never used really old D compiler, but the error looks 
reasonable to me. The following code should compile - note arr is 
"const".

	template Foo(T, T[] arr)
	{
		void boo()
		{
		}
	}

	struct Bar
	{
	}

	void main()
	{
		const Bar[] arr;// = [];
		(Foo!(Bar, arr)).boo();

	}