Hey,
Is there any way to create a macro that allows a Some<T>
or T
as input?
It’s for creating a Span
struct that I’m using:
struct Span {
line: usize,
column: usize,
file_path: Option<String>,
}
…and I have the following macro:
macro_rules! span {
($line:expr, $column:expr) => {
Span {
line: $line,
column: $column
file_path: None,
}
};
($line:expr, $column:expr, $file_path: expr) => {
Span {
line: $line,
column: $column
file_path: Some($file_path.to_string()),
}
};
}
…which allows me to do this:
let foo = span!(1, 1);
let bar = span!(1, 1, "file.txt");
However, sometimes I don’t want to pass in the file path directly but through a variable that is Option<String>. To do this, I always have to match the variable:
let file_path = Some("file.txt");
let foo = match file_path {
Some(file_path) => span!(1, 1, file_path),
None => span!(1, 1),
}
Is there a way which allows me to directly use span!(1, 1, file_path)
where file_path
could be "file.txt"
, Some("file.txt")
or None
?
Thanks in advance!
I made an edit.
There’s not anything stopping it from supporting Option<&str> though. This would be the implementation
impl OptionUpgrade for Option<&str> { fn upgrade(self) -> Option<String> { self.map(|v| v.into()) } }
It’s also possible to just make it generic over Option types
impl<A: ToString> OptionUpgrade for Option<A> { fn upgrade(self) -> Option<String> { self.map(|v| v.to_string()) } }
Yes, but then the concrete type of
None
literals becomes unknown, which is what I was trying to point out.I had commented something similar to stating it was possible to pass the inference problem to the struct if the goal was to support more types, but I removed it because I didn’t think my example was easy to understand when reading it later. I made a better example though
https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=8651fa6121840658b4b6249399f693c7