1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245
#![crate_name = "pad"] #![crate_type = "rlib"] #![crate_type = "dylib"] #![deny(unsafe_code)] #![warn(missing_copy_implementations)] #![warn(missing_debug_implementations)] #![warn(missing_docs)] #![warn(trivial_numeric_casts)] #![warn(unreachable_pub)] #![warn(unused_results)] //! This is a library for padding strings at runtime. //! //! The routines in `std::fmt` only work with formatting strings provided at //! compile-time, making them unsuitable for padding to a custom or //! user-defined value. Rather than re-implement all of `std::fmt`, padding is //! probably the most common use case, which is written in a more //! runtime-friendly fashion here. //! //! It provides four helper functions for the most common use cases, and one //! main function (`pad`) to cover the other cases. //! //! String length is determined with the //! [width](http://doc.rust-lang.org/nightly/std/str/trait.StrExt.html#tymethod.width) //! function, without assuming CJK. //! //! Examples //! -------- //! //! You can pad a string to have a minimum width with the `pad_to_width` //! method: //! //! ```rust //! use pad::PadStr; //! println!("{}", "Hi there!".pad_to_width(16)); //! ``` //! //! This will print out "Hi there!" followed by seven spaces, which is the //! number of spaces necessary to bring it up to a total of sixteen characters //! wide. //! //! //! Alignment //! --------- //! //! By default, strings are left-aligned: any extra characters are added on //! the right. To change this, pass in an `Alignment` value: //! //! ```rust //! use pad::{PadStr, Alignment}; //! let s = "I'm over here".pad_to_width_with_alignment(20, Alignment::Right); //! ``` //! //! There are four of these in total: //! //! - **Left**, which puts the text on the left and spaces on the right; //! - **Right**, which puts the text on the right and spaces on the left; //! - **Middle**, which centres the text evenly, putting it slightly to the //! left if it can't be exactly centered; //! - **MiddleRight**, as above, but to the right. //! //! //! Characters //! ---------- //! //! Another thing that's set by default is the character that's used to pad //! the strings - by default, it's space, but you can change it: //! //! ```rust //! use pad::PadStr; //! let s = "Example".pad_to_width_with_char(10, '_'); //! ``` //! //! //! Truncation //! ---------- //! //! Finally, you can override what happens when a value exceeds the width you //! give. By default, the width parameter indicates a *minimum width*: any //! string less will be padded, but any string greater will still be returned //! in its entirety. //! //! You can instead tell it to pad with a maximum value, which will truncate //! the input when a string longer than the width is passed in. //! //! ```rust //! use pad::PadStr; //! let short = "short".with_exact_width(10); // "short " //! let long = "this string is long".with_exact_width(10); // "this strin" //! ``` //! //! //! A Full Example //! -------------- //! //! All of the above functions delegate to the `pad` function, which you can //! use in special cases. Here, in order to **right**-pad a number with //! **zeroes**, pass in all the arguments: //! //! ```rust //! use pad::{PadStr, Alignment}; //! let s = "12345".pad(10, '0', Alignment::Right, true); //! ``` //! //! (The `true` at the end could just as easily be `false`. It's whether to //! truncate or not.) //! //! //! Note on Debugging //! ----------------- //! //! One very last point: the width function takes a `usize`, rather than a //! signed number type. This means that if you try to pass in a negative size, //! it'll wrap around to a positive size, and produce a massive string and //! possibly crash your program. So if your padding calls are failing for some //! reason, this is probably why. extern crate unicode_width; use unicode_width::UnicodeWidthStr; /// An **alignment** tells the padder where to put the spaces. #[derive(PartialEq, Eq, Debug, Copy, Clone)] pub enum Alignment { /// Text on the left, spaces on the right. Left, /// Text on the right, spaces on the left. Right, /// Text in the middle, spaces around it, but **shifted to the left** if it can't be exactly central. Middle, /// Text in the middle, spaces around it, but **shifted to the right** if it can't be exactly central. MiddleRight, } /// Functions to do with string padding. pub trait PadStr { /// Pad a string to be at least the given width by adding spaces on the /// right. fn pad_to_width(&self, width: usize) -> String { self.pad(width, ' ', Alignment::Left, false) } /// Pad a string to be at least the given width by adding the given /// character on the right. fn pad_to_width_with_char(&self, width: usize, pad_char: char) -> String { self.pad(width, pad_char, Alignment::Left, false) } /// Pad a string to be at least the given with by adding spaces around it. fn pad_to_width_with_alignment(&self, width: usize, alignment: Alignment) -> String { self.pad(width, ' ', alignment, false) } /// Pad a string to be *exactly* the given width by either adding spaces /// on the right, or by truncating it to that width. fn with_exact_width(&self, width: usize) -> String { self.pad(width, ' ', Alignment::Left, true) } /// Pad a string to the given width somehow. fn pad(&self, width: usize, pad_char: char, alignment: Alignment, truncate: bool) -> String; } impl PadStr for str { fn pad(&self, width: usize, pad_char: char, alignment: Alignment, truncate: bool) -> String { use self::Alignment::*; // Use width instead of len for graphical display let cols = UnicodeWidthStr::width(self); if cols >= width { if truncate { return self[..width].to_string(); } else { return self.to_string(); } } let diff = width - cols; let (left_pad, right_pad) = match alignment { Left => (0, diff), Right => (diff, 0), Middle => (diff / 2, diff - diff / 2), MiddleRight => (diff - diff / 2, diff / 2), }; let mut s = String::new(); for _ in 0..left_pad { s.push(pad_char) } s.push_str(self); for _ in 0..right_pad { s.push(pad_char) } s } } #[cfg(test)] mod test { use super::PadStr; use super::Alignment::*; macro_rules! test { ($name: ident: $input: expr => $result: expr) => { #[test] fn $name() { assert_eq!($result.to_string(), $input) } }; } test!(zero: "".pad_to_width(0) => ""); test!(simple: "hello".pad_to_width(10) => "hello "); test!(spaces: "".pad_to_width(6) => " "); test!(too_long: "hello".pad_to_width(2) => "hello"); test!(still_to_long: "hi there".pad_to_width(0) => "hi there"); test!(exact_length: "greetings".pad_to_width(9) => "greetings"); test!(one_more: "greetings".pad_to_width(10) => "greetings "); test!(one_less: "greetings".pad_to_width(8) => "greetings"); test!(left: "left align".pad_to_width_with_alignment(13, Left) => "left align "); test!(right: "right align".pad_to_width_with_alignment(13, Right) => " right align"); test!(centre_even: "good day".pad_to_width_with_alignment(12, Middle) => " good day "); test!(centre_odd: "salutations".pad_to_width_with_alignment(13, Middle) => " salutations "); test!(centre_offset: "odd".pad_to_width_with_alignment(6, Middle) => " odd "); test!(centre_offset_2: "odd".pad_to_width_with_alignment(6, MiddleRight) => " odd "); test!(character: "testing".pad_to_width_with_char(10, '_') => "testing___"); test!(accent: "pâté".pad_to_width(6) => "pâté "); test!(truncate: "this song is just six words long".with_exact_width(7) => "this so"); test!(too_short: "stormclouds".with_exact_width(15) => "stormclouds "); }