I forgot to mention the greatest thing that happened in Advent of Code day 7, when the "filesystem" my code produced didn't have quite enough stuff in it (because I was not handling the first thing I saw in each directory correctly).
I was getting despondent that I'd have to write some output code to show a nicely indented directory tree. But, as a first step, I added dbg!(filesystem); to my code.
The dbg! macro is a really ergonomic form of print debugging: it prints out the line number you're on, the expression inside, and the expression's value, using a formatter that can be "derived" (automatically implemented) for most types. I figured it would be a mess that maybe I could squint at and understand the structure, like a Python repr(). What I got was
[src/main.rs:215] filesystem = Dir {
contents: {
"b.txt": File {
size: 14848514,
},
"d": Dir {
contents: {
"d.log": File {
size: 8033020,
},
"k": File {
size: 7214296,
},
"d.ext": File {
size: 5626152,
},
},
},
"c.dat": File {
size: 8504156,
},
"a": Dir {
contents: {
"h.lst": File {
size: 62596,
},
"g": File {
size: 2557,
},
},
},
},
}
It's the filesystem! It's indented in a way that's really readable! The automatic implementation of Debug I got for a type I had just defined is that good.
I quickly found the missing file entries and fixed the problem. Thanks, Rust.
