SE-0200 first entered review in March 2018. At the same time, the feature set the standard for what Swift “raw” strings should look like. They support escapes, including interpolation, unicode character insertion, and so forth. Multi-line literals did not lose any of Swift’s string power. In introducing the new delimiter and multi-line support, new-line and quote marks can be used without escapes, taking the first steps forward towards better literals.
The resulting string literal is clear, readable, and inspectable. Quote and newline backslashes evaporate in the new syntax. "Or else what?" said Alice, for the Knight had made a sudden pause. "Either it brings tears to their eyes, or else -" Since multi-line strings used three quotes """ to start and end literals, they allowed individual quote marks and new lines without escape sequences. SE-0168 Multi-Line String Literals not only introduced a way to create string literals with more than one line and no new-line escapes, it also provided a hint of the direction the Swift language would take in terms of custom delimiters. This feature allows variations of the delimiter to be included within the string, allowing more expressive raw string content. Rust and Java go beyond this to allow customizable delimiters. Most languages adopt a prefix (like q, R, or r) to indicate raw content. """hello \' world""" and raw"Hello, world!"
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Its content continues until it reaches the string’s end delimiter, which varies by language, as in the following table: Syntaxīourne shell, Perl, PHP, Ruby, Windows PowerShell A raw string does not interpret escape sequences. Raw strings are used in many languages including C#, Perl, Rust, Python, Ruby, and Scala.
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This feature is used in applications that produce code output, that work with regular expressions, that use in-app source code (for example, when interactively teaching a language), and for pre-escaped domain-specific content like JSON and XML. In a raw string, \n represents the backslash character followed by the letter n rather than a line feed. “world” is indented by a single tab:Ī raw string, in contrast, ignores escape sequences and treats all content as literal characters. It is one of the language’s highlights.įor example, the string literal "hello\n\n\tworld" consists of three lines, with “hello” on the first and “world” on the third. Swift’s interpolation feature offers a powerful and compiler-checked way to add content to strings. Interpolated expressions, introduced by \( and terminated by ).Escape SequencesĮscape sequences are backslash-prepended combinations like \\, \", and \u, where n is a 1–8 digit hexadecimal number with a value equal to a valid Unicode code point
This post discusses what raw strings are, how Swift designed its take on this technology, and how you can use this new Swift 5 feature in your code. It ended with a uniquely Swift take on “raw strings” that focused on adding custom delimiters to string literals and escape sequences. The development, refinement, and deployment of SE-0200 Enhancing String Literals Delimiters to Support Raw Text was a long and surprising journey.
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