I found a lot of the Phobos documentation to contain template arguments and if statements that made no sense to me, for example:

```
 uint readf(alias format, A...) (
 auto ref A args
)
if (isSomeString!(typeof(format)));

uint readf(A...) (
 scope const(char)[] format,
 auto ref A args
);
``` https://dlang.org/library/std/stdio/file.readf.html

From stdio.readf & stdio.File.readf. I'm assuming this is some kind of template, but often it seems there are more parameters in the first '()' part than are ever given. Am I missing something? Additionally, what is that if statement for? It precedes nothing.

On Sunday, 20 December 2020 at 13:51:08 UTC, Rekel wrote:
> I found a lot of the Phobos documentation to contain template arguments and if statements that made no sense to me, for example:
>
> ```
>  uint readf(alias format, A...) (
>  auto ref A args
> )
> if (isSomeString!(typeof(format)));
>
> uint readf(A...) (
>  scope const(char)[] format,
>  auto ref A args
> );
> ``` https://dlang.org/library/std/stdio/file.readf.html
>
> From stdio.readf & stdio.File.readf. I'm assuming this is some kind of template, but often it seems there are more parameters in the first '()' part than are ever given. Am I missing something? Additionally, what is that if statement for? It precedes nothing.

The if is a template constraint.

On Sunday, 20 December 2020 at 13:58:00 UTC, Max Haughton wrote:
> The if is a template constraint.

Ah sorry! I must have missed that part of the dlang tour.
(https://tour.dlang.org/tour/en/gems/template-meta-programming)

Thanks a lot!