If my library is declared as no_std, can I use std for my integration tests, or could that implicitly change something in the library? I found this similar question, which implies that using std is ok in such a situation, but it doesn't explicitly answer my question.
Does the answer to my question change if I'm using build-std for a custom target instead of a prebuilt std library?
No, your library will not be affected by the crates that depend on it. That would be a horrible world.
Related
Looking at some crates in https://crates.io/ I found that rand is the most downloaded crate and looking in it's dependencies I found the libc crate and in it's dependencies I found the rustc-std-workspace-core which has 0 dependencies
with this description: "Explicitly empty crate for rust-lang/rust integration". I could not totally undestand what it means. Can someone explain in more details?
std depends on the libc crate.
Being a dependency of std is... not easy. The way std is built is complicated, it is tightly coupled with the compiler and built with it twice, for bootstrapping.
You can see this dependency is only activated if the rustc-dep-of-std feature is enabled.
This dependency allows std to depend on crates.
See also Plan for removal of rustc-dep-of-std.
I am exploring the option to dynamically load libraries at runtime in Rust. I am still a Rust newbie, so I found several articles detailing why this is not the recommended way.
Plugins in Rust
Dynamically Loading Plugin
Rust has no stable ABI
I have not found, or maybe have not fully understood why this is so? Rust is a systems programming language to my understanding, and such, isn't dynamic loading and plugin writing important to this goal?
Is there a meaningful design decision behind Rust's static compiling be default?
As a side note: I have found a crate that supports this pretty well, but before using it I would like to understand why the Rust creators would rather not build this into the language.
I come from a Java background and have recently started with Rust.
The official Rust doc is pretty self-explanatory except the chapter that explains Crates and Packages.
The official doc complicates it with so many ORs and ANDs while explaining the two.
This reddit post explains it a little better, but is not thorough.
What is the exact difference between a Crate and Package in Rust? Where/When do we use them?
Much thanks!
Crates
From the perspective of the Rust compiler, "crate" is the name of the compilation unit. A crate consists of an hierarchy of modules in one or multiple files. This is in contrast to most "traditional" compiled languages like Java, C or C++, where the compilation unit is a single file.
From the perspective of an user, this definition isn't really helpful. Indeed, in most cases, you will need to distinguish between two types of crates:
binary crates can be compiled to executables by the Rust compiler. For example, Cargo, the Rust package manager, is a binary crate translated by the Rust compiler to the executable that you use to manage your project.
library crates are what you'd simply call libraries in other languages. A binary crate can depend on library crates to use functionality supplied by the libraries.
Packages
The concept of packages does not originate in the Rust compiler, but in Cargo, the Rust package manager. At least for simple projects, a package is also what you will check into version control.
A package consists of one or multiple crates, but no more than one library crate.
Creating packages
to create a new package consisting of one binary crate, you can run cargo new
to create a new package consisting of one library crate, you can run cargo new --lib
to create a package consisting of a library as well as one or multiple binaries, you can run either cargo new or cargo new --lib and then modify the package directory structure to add the other crate
When should you use crates, and when should you use packages?
As you can see now, this question doesn't really make sense – you should and must always use both. A package can't exist without at least one crate, and a crate is (at least if you are using Cargo) always part of a package.
Therefore, a better question is this:
When should you put multiple crates into one package?
There are multiple reasons to have more than one crate in a package. For example:
If you have a binary crate, it is idiomatic to have the "business logic" in a library in the same package. This has multiple advantages:
Libraries can be integration tested while binaries can't
If you later decide that the business logic needs to also be used in another binary, it is trivial to add this second binary to the package and also use the library
If you have a library crate that generates some files (a database engine or something like that), you may want to have a helper binary to inspect those files
Note that if you have a very big project, you may instead want to use the workspace feature of Cargo in these cases.
I need a class with functionality equal to vector<bool> in C++. The Rust documentation tells about BitVec, but use std::collections::BitVec causes Unresolved import error during compiling. According to a pull request, BitVec has been removed. Is there any adequate replacement for it?
There does not exist a dedicated bit-vector in the standard library and Vec<bool> is not specialized like C++'s vector<bool>. Rust advocates the use of external crates instead of building a huge standard library. The de-facto crate for this use case is bit-vec.
You appear to have found a link to an old standard library documentation: https://doc.rust-lang.org/1.2.0/std/collections/struct.BitVec.html. Note the 1.2.0 in the url! The current version of Rust is 1.25 (as of April 2018), which means that 1.2 is already more than two years old. Apart from that, BitVec is marked as unstable in the 1.2 docs; it was removed later.
In C++, you could use something like __clang_version__. Is there something similar for Rust? I searched on the internet, but found nothing.
Not directly.
There is the rustc_version crate which tells you the version of rustc accessible on the command-line; this is designed to be used in a build script. There's also rustc_version_runtime which does something similar, but exposes the information as a runtime call (i.e. it detects the compiler version at compile time, but exposes it at runtime).
Standard disclaimer: be very careful writing anything that depends on compiler version. You should ideally only test for minimum versions for which features are supported using semver (which both of the above libraries support directly).