On Thursday, 1 January 2026 at 17:01:25 UTC, zhade wrote:
Hi, I am trying to fail-fast and need to return "something"
that works together with MapResult.
I came up with a solution but wanted to know if its the
supposed way to do it.
What I learned is that the lambdas of `map` and `filter` are
part of the return type.
`MapResult` does not have an universal empty value. If you want
its result to be empty, you need to give it a source range that
is also empty. Fortunately, in your case it is easy to do:
```d
auto example_func(bool fail)
{
auto list = fail? []: someExpensiveOperation();
return list
.filter!(a => a != "expensive")
.map!(a => tuple!("value", "numLetters")(a, a.length));
}
```
You could also iterate the result range until it's empty before
returning it, but that's wasting CPU cycles.
