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September 26, 2014 00:03
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Python list comprehensions in Rust
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#![feature(macro_rules)] | |
/// MIT license etc. etc. | |
/// | |
/// Experimenting with Python-like list comprehensions. | |
/// | |
/// An attempt to explore the possibility space for ergonomic improvements | |
/// in Rust that can come post v1.0. Notice that there are not type declerations. | |
/// Aside from the "c!" macro invocation, Rust allows for an exact copy of the | |
/// Python comprehension syntax. | |
/// | |
/// This should probably work on slices. Something to look forward to. | |
use std::num::{abs, pow}; // Used in unit tests only. | |
macro_rules! c( | |
($m:expr for $el:ident in $iter:expr) => ( | |
{ | |
let (lower, upper) = $iter.size_hint(); | |
let mut result = match upper { | |
Some(bound) => Vec::with_capacity(bound), | |
None => Vec::with_capacity(lower), | |
}; | |
for $el in $iter { | |
let $el = $el.clone(); | |
result.push($m); | |
} | |
result | |
} | |
); | |
($m:expr for $el:ident in $iter:expr if $cond:expr) => ( | |
{ | |
let mut result = Vec::new(); | |
for $el in $iter { | |
let $el = $el.clone(); | |
if $cond { | |
result.push($m); | |
} | |
} | |
result | |
} | |
); | |
($m:expr for $el:ident in $iter:expr | |
$(for $inner_el:ident in $inner_iter:expr)* | |
$(if $cond:expr)*) => ( | |
{ | |
let mut result = Vec::new(); | |
for $el in $iter { | |
let $el = $el.clone(); | |
result.push_all_move(c!($($m for $inner_el in $inner_iter)+ $(if $cond)*)); | |
} | |
result | |
} | |
); | |
) | |
#[test] | |
fn simple_comprehension() { | |
let squares = c![ x * x for x in range(0, 10i) ]; | |
assert_eq!(squares, vec![0i, 1, 4, 9, 16, 25, 36, 49, 64, 81]); | |
} | |
#[test] | |
fn vector_to_iter_comprehension() { | |
let vec = vec![-4i, -2, 0, 2, 4]; | |
let output: Vec<int> = c![x*2 for x in vec.iter()]; | |
assert_eq!(output, vec![-8i, -4, 0, 4, 8]); | |
} | |
#[test] | |
fn filter_comprehension() { | |
let vec = vec![-4i, -2, 0, 2, 4]; | |
let output = c![x for x in vec.iter() if x >= 0i]; | |
assert_eq!(output, vec![0i, 2, 4]); | |
} | |
#[test] | |
fn apply_function_comprehension() { | |
let vec = vec![-4i, -2, 0, 2, 4]; | |
let output = c![abs(x) for x in vec.iter()]; | |
assert_eq!(output, vec![4i, 2, 0, 2, 4]); | |
} | |
#[test] | |
fn call_method_comprehension() { | |
let fresh_fruit = vec![" banana", " loganberry ", "passion fruit "]; | |
let output = c![fruit.trim_chars(' ') for fruit in fresh_fruit.iter()]; | |
assert_eq!(output, vec!["banana", "loganberry", "passion fruit"]); | |
} | |
#[test] | |
fn change_type_comprehension() { | |
let output = c![(x, pow(x,2)) for x in range(0i,6)]; | |
assert_eq!(output, vec![(0i, 0i), (1, 1), (2, 4), (3, 9), (4, 16), (5, 25)]); | |
} | |
#[test] | |
fn combined_comprehension() { | |
let a = vec![1i,2,3]; | |
let b = vec![3i,1,4]; | |
let not_equal = c![(x, y) for x in a.iter() for y in b.iter() if x != y]; | |
assert_eq!(not_equal, vec![(1i, 3i), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]); | |
println!("{}", a); | |
} | |
#[test] | |
fn nested_comprehensions() { | |
let matrix = vec![vec![1i,2,3,4],vec![5,6,7,8],vec![9,10,11,12]]; | |
let output = c![ c![ row[i] for row in matrix.iter()] for i in range(0u,4)]; | |
assert_eq!(output, vec![vec![1i,5,9], vec![2i,6,10], vec![3i,7,11], vec![4i,8,12]]); | |
} |
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