Clever system !

Posted Dec 5, 2024 7:31 UTC (Thu) by samlh (subscriber, #56788)
In reply to: Clever system ! by Karellen
Parent article: Rust's incremental compiler architecture

[...]what is the difference between a crate and a library?

To keep it short:

A crate is the rust unit of compilation, composed of 1 or more rust source files
Crates can be compiled as libraries or executables
Library crates get compiled to a .rlib file which contains compiled binary code along with metadata for:
- exported apis, static variables, constants, etc
- generic function implementations (in a partially compiled form)
- other stuff :) [for example, when LTO is involved, the rlib can contain LLVM bitcode]
Think of .rlibs as equivalent to a C++ static library + header files + linking instructions.
The .rlib format (and the Rust abi more generally) is not stable across compiler releases, so .rlib files are usually treated as temporary artifacts (similar to .o files).
When compiling the final executable, the binary code from the rlibs are statically linked together, along with instantiations of the imported generic functions (as needed).
It is also possible to compile crates as C-style static libraries (libfoo.a) or shared objects (libfoo.so). This is often done in order to expose a stable C-compatible abi to be used externally.