#derive #vec #fromstr #iterator #vector

macro collections-fromstr

Derives FromStr for collection types like Vec or HashSet

2 releases

0.1.1 May 14, 2021
0.1.0 May 14, 2021

#1018 in Rust patterns

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This crate provides a FromStr derive for newtypes on iterable collections on single types, such Vec<T> or HashSet<T>. The element is parsed by splitting the input along a pattern that you specify though the #[item_separator] attribute. The individual items are then parsed using their respective FromStr implementations.


  • The macro will take the first field in your struct that has a type with a path argument <T> and assume that it is the inner type. It will assume that T in this example is the item type.
  • The item type T must not be an actual type (no trait type) that implements FromStr.
  • As inner type you can use any type that implements FromIterator<Item = T> (like Vec<T> or HashSet<T>).
  • From needs to be implemented between your newtype and its inner type. Crates like derive_more take easy care of that.


use collections_fromstr::FromStr;
use derive_more::From;
use std::str::FromStr;

#[derive(From, FromStr, PartialEq)]
#[item_separator = ","]
struct NewVec(Vec<i32>);

static VALUES: &str = "1,2,3,-3,-2,-1";
    NewVec::from_str(VALUES).unwrap() == NewVec(vec![1,2,3,-3,-2,-1])

Wait... you know that I could just use Iterator::split for this, right?

Okay, hear me out. Say you've got data like this:

1-3:B,I,U//43-60:I//83-87:I,U//99-104: B,I// [etc.]

Let's say this data represents text markup: You've got character ranges on the left of the colon :, and highlighting information on the right side (B = bold, I = italics, U = underline, but you'll probably expand it later once you get that hedgefund money), of which there might be multiple, separated by commas ,. Each markup is separated by double slashes //.

... Now look at the magic of FromStr doing its thing:

use std::collections::HashSet;
use derive_more::From;
use std::ops::Range;

struct CharRange(#[from_str(default)] Range<u32>);

#[derive(parse_display::FromStr, Hash, PartialEq, Eq)]
enum MarkupOperation {

#[derive(From, collections_fromstr::FromStr)]
struct Operations(HashSet<MarkupOperation>);

struct Markup{
    range: CharRange,
    operations: Operations,

#[derive(From, collections_fromstr::FromStr)]
struct MarkupVec(Vec<Markup>);

Look at this code. It's. So. Clean. 🥺 You'll also be less likely to produce bugs, like forgetting about the case of an empty input string.


collections-fromstr is distributed under the terms of both the MIT license and the Apache License (Version 2.0).



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