Can you explain the .map(drop) in usage example? about color-eyre

[fleetingbytes]

Thank you very much for the thorough explanation. It helped me to learn a great deal of rust basics as I followed the paths in this rabbit hole.

[yaahc]

Happy to explain!

The drop there is referring to std::mem::drop¹, which is a free function in the prelude² not a closure.

The reason this works with map is because map expects any arbitrary type that implements the FnOnce(T) -> U trait, which is implemented automatically for both closures and for functions or even for any arbitrary type on nightly if you enable the fn_traits feature and implement FnOnce manually. The end result is that drop ends up being called on the String from the previous function in the Ok case which just throws it away and replaces it with the unit type () aka nothing.

Footnotes

1. https://doc.rust-lang.org/stable/std/mem/fn.drop.html ↩

2. https://doc.rust-lang.org/stable/std/prelude/index.html ↩