Why is there a mod keyword in Rust?

Question

After reading this I'm wondering why is there "mod" keyword and mod.rs? The folder hierarchy can describe the module as well?

Answer 1

While it can, it can also be overridden:

#[path = "somewhere/else"]
mod lol;

Answer 2

There are a couple of reasons why modules must be explicitly declared:

• Modules can be public (pub mod foo;) or private (mod foo;).

• They can have attributes applied to them, attributes that couldn’t sit inside the file; there are two primary examples of that: #[path = "x.rs"] specifying a different path, and #[cfg(…)], for conditional compilation, for cases where the module would fail to parse or have its macros expand.