textwrap-0.13.0

This is a major release which rewrites the core logic, adds many new features, and fixes a couple of bugs. Most programs which use textwrap stays the same, incompatibilities and upgrade notes are given below.

Clone the repository and run the following to explore the new features in an interactive demo (Linux only):

$ cargo run --example interactive --all-features

Bug Fixes

Rewritten core wrapping algorithm

• #221: Reformulate wrapping in terms of words with whitespace and penalties.

The core wrapping algorithm has been completely rewritten. This fixed bugs and simplified the code, while also making it possible to use textwrap outside the context of the terminal.

As part of this, trailing whitespace is now discarded consistently from wrapped lines. Before we would inconsistently remove whitespace at the end of wrapped lines, except for the last. Leading whitespace is still preserved.

New Features

Optimal-fit wrapping

• #234: Introduce wrapping using an optimal-fit algorithm.

This release adds support for new wrapping algorithm which finds a globally optimal set of line breaks, taking certain penalties into account. As an example, the old algorithm would produce

"To be, or"
"not to be:"
"that is"
"the"
"question"

Notice how the fourth line with “the” is very short. The new algorithm shortens the previous lines slightly to produce fewer short lines:

"To be,"
"or not to"
"be: that"
"is the"
"question"

Use the new textwrap::core::WrapAlgorithm enum to select between the new and old algorithm. By default, the new algorithm is used.

The optimal-fit algorithm is inspired by the line breaking algorithm used in TeX, described in the 1981 article Breaking Paragraphs into Lines by Knuth and Plass.

In-place wrapping

• #226: Add a fill_inplace function.

When the text you want to fill is already a temporary String, you can now mutate it in-place with fill_inplace:

let mut greeting = format!("Greetings {}, welcome to the game! You have {} lives left.",
                           player.name, player.lives);
fill_inplace(&mut greeting, line_width);

This is faster than calling fill and it will reuse the memory already allocated for the string.

Changed Features

Wrapper is replaced with Options

• #213: Simplify API with only top-level functions.
• #215: Reintroducing the type parameter on Options (previously known as Wrapper).
• #219: Allow using trait objects with fill & wrap.
• #227: Replace WrapOptions with Into<Options>.

The Wrapper struct held the options (line width, indentation, etc) for wrapping text. It was also the entry point for actually wrapping the text via its methods such as wrap, wrap_iter, into_wrap_iter, and fill methods.

The struct has been replaced by a simpler Options struct which only holds options. The Wrapper methods are gone, their job has been taken over by the top-level wrap and fill functions. The signature of these functions have changed from

fn fill(s: &str, width: usize) -> String;

fn wrap(s: &str, width: usize) -> Vec<Cow<'_, str>>;

to the more general

fn fill<'a, S, Opt>(text: &str, options: Opt) -> String
where
    S: WordSplitter,
    Opt: Into<Options<'a, S>>;

fn wrap<'a, S, Opt>(text: &str, options: Opt) -> Vec<Cow<'_, str>>
where
    S: WordSplitter,
    Opt: Into<Options<'a, S>>;

The Into<Options<'a, S> bound allows you to pass an usize (which is interpreted as the line width) and a full Options object. This allows the new functions to work like the old, plus you can now fully customize the behavior of the wrapping via Options when needed.

Code that call textwrap::wrap or textwrap::fill can remain unchanged. Code that calls into Wrapper::wrap or Wrapper::fill will need to be update. This is a mechanical change, please see #213 for examples.

Thanks to @Cryptjar and @Koxiat for their support in the PRs above!

Removed Features

• The wrap_iter and into_wrap_iter methods are gone. This means that lazy iteration is no longer supported: you always get all wrapped lines back as a Vec. This was done to simplify the code and to support the optimal-fit algorithm.

  The first-fit algorithm could still be implemented in an incremental fashion. Please let us know if this is important to you.

Other Changes

• #206: Change Wrapper.splitter from T: WordSplitter to Box<dyn WordSplitter>.
• #216: Forbid the use of unsafe code.