Lazy
separator.join(iterable)method andlazy_format!for Rust
Add the following line to your Cargo.toml, under [dependencies]
toml
join-lazy-fmt = "0.9.0"
Add the folowing line to your .rs code to bring items in scope:
rust
use ::join_lazy_fmt::*;
```rust,edition2018 use ::joinlazyfmt::*;
let sequence = format!("[{}]", ", ".join(0 .. 5)); assert_eq!(sequence, "[0, 1, 2, 3, 4]");
// Since .join() is lazy, this does not compute an infinite string.
let _ = ", ".join(0 ..);
const N: usize = 6;
let line = format!("+-{}-+", "-+-".join((1 .. N).map(|| "---")));
// And the following allocates only one String:
let matrix = format!(
"{line}\n{body}\n{line}\n",
line=line,
body="\n".join(
(1 .. N).map(|i| lazyformat!(
"| {row} |",
row=" | ".join(
(1 .. N).map(|j| lazyformat!(
"a{i}{j}",
i=i,
j=j,
))
),
))
),
);
asserteq!(matrix, "\
+-----+-----+-----+-----+-----+
| a11 | a12 | a13 | a14 | a15 |
| a21 | a22 | a23 | a24 | a25 |
| a31 | a32 | a33 | a34 | a35 |
| a41 | a42 | a43 | a44 | a45 |
| a51 | a52 | a53 | a54 | a55 |
+-----+-----+-----+-----+-----+
");
```