#macros #function #generics #ndarray #iterator


A macro for easier writing of functions that accept any string-, path-, iterator-, array-, or ndarray-like input

7 releases

Uses new Rust 2021

0.1.6 Oct 20, 2022
0.1.5 Oct 11, 2022

#196 in Rust patterns

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github crates.io docs.rsCI

A macro for easier writing of functions that accept any string-, path-, iterator-, array-, or ndarray-like input

Do you know how to write a function that accepts any kind of string as input? (Are you sure it accepts, for example, a borrowed reference to String?) Do you know how to accept any kind of iterator? How about an iterator of any kind of path? How about a function that accepts a Vec<f32> as a ndarray::ArrayView1? If yes, you don't need this crate.

Rust functions can accept all these inputs, but the syntax can be hard to remember and read. This crate provides syntactic sugar that makes writing and reading such functions easier.

The AnyInputs are AnyString, AnyPath, AnyIter, AnyArray, and (optionally) AnyNdArray. They may be nested.



Add this to your Cargo.toml:

anyinput = { version = "0.1.6", features = ["ndarray"] }

If you don't need NdArray support, omit the ndarray feature.


We'll start with examples that are so simple that you may not need the macro. We want to show that simple examples stay simple.

Create a function that adds 2 to the length of any string-like thing.

use anyinput::anyinput;

fn len_plus_2(s: AnyString) -> usize {

// By using AnyString, len_plus_2 works with
// &str, String, or &String -- borrowed or moved.
assert_eq!(len_plus_2("Hello"), 7); // move a &str
let input: &str = "Hello";
assert_eq!(len_plus_2(&input), 7); // borrow a &str
let input: String = "Hello".to_string();
assert_eq!(len_plus_2(&input), 7); // borrow a String
let input2: &String = &input;
assert_eq!(len_plus_2(&input2), 7); // borrow a &String
assert_eq!(len_plus_2(input2), 7); // move a &String
assert_eq!(len_plus_2(input), 7); // move a String

Another simple example: Create a function that counts the components of any path-like thing.

use anyinput::anyinput;
use std::path::Path;

fn component_count(path: AnyPath) -> usize {

// By using AnyPath, component_count works with any
// string-like or path-like thing, borrowed or moved.
assert_eq!(component_count("usr/files/home"), 3);
let path = Path::new("usr/files/home");
assert_eq!(component_count(&path), 3);
let pathbuf = path.to_path_buf();
assert_eq!(component_count(pathbuf), 3);

As we add nesting and multiple inputs, the macro becomes more useful. Here we create a function with two inputs. One input accepts any iterator-like thing of usize. The second input accepts any iterator-like thing of string-like things. The function returns the sum of the numbers and string lengths.

We apply the function to the range 1..=10 and a slice of &str's.

use anyinput::anyinput;

fn two_iterator_sum(iter1: AnyIter<usize>, iter2: AnyIter<AnyString>) -> usize {
    let mut sum = iter1.sum();
    for any_string in iter2 {
        // Needs .as_ref to turn the nested AnyString into a &str.
        sum += any_string.as_ref().len();

assert_eq!(two_iterator_sum(1..=10, ["a", "bb", "ccc"]), 61);

Create a function that accepts an array-like thing of path-like things. Return the number of path components at an index.

use anyinput::anyinput;
use anyhow::Result;

fn indexed_component_count(
    array: AnyArray<AnyPath>,
    index: usize,
) -> Result<usize, anyhow::Error> {
    // Needs .as_ref to turn the nested AnyPath into a &Path.
    let path = array[index].as_ref();
    let count = path.iter().count();

    indexed_component_count(vec!["usr/files/home", "usr/data"], 1)?,
# // '# OK...' needed for doctest
# Ok::<(), anyhow::Error>(())

You can easily apply NdArray functions to any array-like thing of numbers. For example, here we create a function that accepts an NdArray-like thing of f32 and returns the mean. We apply the function to both a Vec and an Array1<f32>.

Support for NdArray is provided by the optional feature ndarray.

use anyinput::anyinput;
use anyhow::Result;

# // '#[cfg...' needed for doctest
# #[cfg(feature = "ndarray")]
fn any_mean(array: AnyNdArray<f32>) -> Result<f32, anyhow::Error> {
    if let Some(mean) = array.mean() {
    } else {
        Err(anyhow::anyhow!("empty array"))

// 'AnyNdArray' works with any 1-D array-like thing, but must be borrowed.
# #[cfg(feature = "ndarray")]
assert_eq!(any_mean(&vec![10.0, 20.0, 30.0, 40.0])?, 25.0);
# #[cfg(feature = "ndarray")]
assert_eq!(any_mean(&ndarray::array![10.0, 20.0, 30.0, 40.0])?, 25.0);
# // '# OK...' needed for doctest
# Ok::<(), anyhow::Error>(())

The AnyInputs

AnyInput Description Creates Concrete Type
AnyString Any string-like thing &str
AnyPath Any path-like or string-like thing &Path
AnyIter Any iterator-like thing <I as IntoIterator>::IntoIter
AnyArray Any array-like thing &[T]
AnyNdArray Any 1-D array-like thing (borrow-only) ndarray::ArrayView1<T>

Notes & Features

  • Suggestions, feature requests, and contributions are welcome.

  • Works with nesting, multiple inputs, and generics.

  • Automatically and efficiently converts an top-level AnyInput into a concrete type.

  • Elements of AnyArray, AnyIter, and AnyNdArray must be a single type. So, AnyArray<AnyString> accepts a vector of all &str or all String, but not mixed.

  • When nesting, efficiently convert the nested AnyInput to the concrete type with

    • .as_ref() -- AnyString, AnyPath, AnyArray
    • .into_iter() -- AnyIter
    • .into() -- AnyNdArray

    (The iterator and array examples above show this.)

  • Let's you easily apply NdArray functions to regular Rust arrays, slices, and Vecs.

  • Used by bed-reader (genomics crate) and fetch-data (sample-file download crate).

How It Works

The #[anyinput] macro uses standard Rust generics to support multiple input types. To do this, it rewrites your function with the appropriate generics. It also adds lines to your function to efficiently convert from any top-level generic to a concrete type. For example, the macro transforms len_plus_2 from:

use anyinput::anyinput;

fn len_plus_2(s: AnyString) -> usize {


fn len_plus_2<AnyString0: AsRef<str>>(s: AnyString0) -> usize {
    let s = s.as_ref();
    s.len() + 2

Here AnyString0 is the generic type. The line let s = s.as_ref() converts from generic type AnyString0 to concrete type &str.

As with all Rust generics, the compiler creates a separate function for each combination of concrete types used by the calling code.


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