Method chaining doesn't free owned strings when not bound?

1

Take this example:

let mut buf = String::new();
std::io::stdin().read_line(&mut buf).unwrap();
let input: Vec<&str> = buf.trim().to_lowercase().split_whitespace().collect();

trim returns a string slice then to_lowercase takes that and returns a new owned string, let's call it X, then split_whitespace takes that and returns and iterator then we collect it into a vector of slices.

This surprisingly works, what happened to X that was produced by to_lowercase? it wasn't bound to any variable, so basically the entries of Input are slices referencing a string that we can't access and don't even know where it is.

Why wasn't it dropped? and where can I read more about this behavior?

2

The string is a temporary inside the expression and is dropped at the end of the statement. Mara has a rather in-depth blog post about temporaries and their behaviour.

5 Likes
3

I just tried to print it afterwards, it invalidated the input as it should've, I forgot to print it afterwards to see if input is actually valid, so X had to be captured by some variable in order for the slices of it to be valid, Thanks.

EDIT: I just found out the only reason it compiled was because input wasn't being used afterwards.

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