Why whitespace is been removed after wrap?

[linrongbin16]

Hi, thanks to your work, I have a simple question:

For example, we have the origin line: "Hello World" (length: 11), after using textwrap::wrap(&line, 10) method, the results are:

["Hello", "World"]

But why the whitespace " " (between "Hello" and "World") is been removed? Is there any options that I could keep the origin text not been changed?

[mgeisler]

Good question! The whitespace at the ends of the lines is removed since it's normally unwanted.

The idea is that each line now takes up at most 10 columns. If the trailing whitespace was left there, then this would not be true.

It goes further than this: the whitespace between the words is attached to the left word, and it is removed at the end of lines. So running

pub fn main() {
    dbg!(textwrap::wrap("This   is   a    demo   ", 10));
}

gives me

[/app/example.rs:2:5] textwrap::wrap("This   is   a    demo   ", 10) = [
    "This   is",
    "a    demo",
]

See https://godbolt.org/z/Kn9GTPvoM for an example of this (the normal Playground gives me an error right now).

What happens is that the text is split into words using the WordSeparator. The default looks for Unicode break points, but you can also just split on ASCII space. The example shows you how the whitespace is attached to the left word:

let words = AsciiSpace.find_words("Hello World!").collect::<Vec<_>>();
assert_eq!(words, vec![Word::from("Hello "), Word::from("World!")]);

To keep the trailing whitespace, you would need to construct your own Words. Unfortunately, I just now realize that it is not possible to easily do this because the width field is private...

You could implement Fragment yourself, but then you need to call the low-level wrapping functions yourself.

Let me try and fix this for the next version!

[linrongbin16]

thanks for your detailed explain!