On Wednesday, 22 November 2023 at 17:53:15 UTC, Antonio wrote:
Basically, it doesn't know witch version of ```filter``` to
use, because it is inferring `i=>i%2==0` is `void` ?!?!?!
```
!()(IIterable!int, void)
```
If I explicitly write `(int i)=>i%2==0`, it compiles correctly
again.
**Is it mandatory to explicitly tell that `S` is `int` when
```IIterable!S source``` is `IIterable!int` alredy?**
This is a bug/limitation in the compiler. I couldn't find an
existing report on issues.dlang.org, so I've reported it myself
as [issue 24255][1].
For now, I think the best way to work around it is to specify the
type in the lambda, as in `(int i) => i%2 == 0`.
The reason you see `void` is that when the compiler cannot figure
out the type of a function literal, it treats it as a template
function:
```d
static assert(__traits(isTemplate, i => i % 2 == 0));
```
And for silly historical reasons, when the compiler tries to
determine the type of a template, it returns `void` instead of
giving an error:
```d
template example() {}
static assert(is(typeof(example) == void)); // what??
```
[1]: https://issues.dlang.org/show_bug.cgi?id=24255
