Linq in Rust

Linq query in Rust (created by declarative macros).

• Inspired by LINQ in .NET.
• What's LINQ

This project is under development! API might be changed.

Quick Start

This is an example:

use linq::linq;

fn try_linq(){
    let x = 1..100;

    let mut y: Vec<i32> = x.clone().filter(|p| p <= &5).collect();
    y.sort_by_key(|t| -t);
    let y: Vec<i32> = y.into_iter().map(|t| t * 2).collect();

    let e: Vec<i32> =
        linq!(from p in x.clone(), where p <= &5, orderby -p, select p * 2).collect();
    
    assert_eq!(e, y);
}

If you are familier with LINQ in C#, you will find this is easy to use.

Usage

The query statement begins with from clause and ends with select clause. Use , to seperate every clause.

linq!(from x in coll, select x)

From

from <id> in <iter expr>,

Also you can enumerate elements of each set in the collection (Attention: for this type, you can't access the value that is in the first from clause in select clause):

let x = 1..5;
let y = vec![0, 0, 1, 0, 1, 2, 0, 1, 2, 3];
let e: Vec<i32> = linq!(from p in x.clone(), from t in 0..p, select t).collect();

assert_eq!(e, y);

If you want to zip or enumerate value-pairs of two sets, use zfrom for the second from:

let x = 1..5;
let y = vec![
    (1, 0),
    (2, 0),
    (2, 1),
    (3, 0),
    (3, 1),
    (3, 2),
    (4, 0),
    (4, 1),
    (4, 2),
    (4, 3),
];
let e: Vec<_> = linq!(from p in x.clone(), zfrom t in 0..p, select (p,t)).collect();

assert_eq!(e, y);

The expression in zfrom recieve the cloned value in the first from, and the elements in two sets will be cloned for select clause.

Where

while <expr>,

You can use where clause in single-from query, and the expression will recieve a variable named the id in from clause. The expression need to return a boolean value.

Orderby

orderby <expr>,
orderby <expr>, descending,

You can use orderby clause in single-from query. This query will collect the iterator, and sort them by the expression, then return the new iterator.

Linq Keywords

• from
  • from (child-from)
  • zfrom (zip-from)
• in
• select
• where
• orderby
• descending
• group_by
• more...

Query Operators

All italic items mean they are not in roadmap. Happy for your suggestions.

All bold items mean they are implemented in this project. You can find them in module linq::ops.

• where => where_by => filter
• select => select_one => map
• select_many => select_many, select_many_zip, select_two
• skip => skip
• skip_while => skip_while
• take => take
• take_while => take_while
• join
• group_join
• concate => chain
• order_by => order_by
• order_by_descending => order_by
• then_by
• then_by_descending
• reverse => rev
• group_by
• distinct
• union
• intersect
• except
• first => next
• single
• element_at => nth
• all => all
• any => any
• contains
• count => count
• sum
• min
• max
• average
• aggregate

Development

We need more unit-test samples. If you have any ideas, open issues to tell us.

Since the expression procedural macros is not stable, I only create macros by declarative macros.

$ cargo test