How to escape characters in json and regex with Swift string

Issue #963

In the world of Swift programming, we often come across situations where we need to work with string literals that contain special characters. These characters can include new lines, tabs, backslashes, and quotes — all of which need to be handled appropriately to ensure they don’t inadvertently affect the structure or behavior of our code. Traditionally, we negate their special meaning by escaping them with backslashes. However, Swift provides an even simpler method — raw strings. Let’s explore how to escape characters in both traditional and raw string literals.

Escaping with Backslashes

In a standard Swift string, the backslash \ is used as an escape character to insert special characters. For instance, when you want to include a quotation mark within a string, you escape it like this:

let string = "\""

This code tells Swift to treat the quote as a literal character in the string rather than the end of the string.

Embracing Convenience with Swift’s Raw Strings

With the introduction of raw strings in Swift, prefixed with a hash mark #, we can directly include special characters without escaping each one:

let rawString = #"""#

This approach not only simplifies the code but also enhances its readability, especially when dealing with regex patterns or JSON strings.

Handling JSON String Literals

When you want to include special characters like new lines or tabs in a JSON string within Swift, look how different the syntax is with and without raw strings:

let jsonString = """
{
    "newline": "\\n"
}
"""

let jsonRawString = #"""
{
    "newline": "\n"
}
"""#

The first jsonString variable depicts a newline escape sequence \\n that must be doubly escaped in a standard string literal. The second json variable with raw string literals requires just a single escape, mirroring the actual JSON representation more accurately.

Special Characters in JSON and Swift

Pay close attention to characters typically used for escaping in JSON, such as the backslash itself. If the goal is to represent the text \] in JSON, you would need to escape the backslash:

{
    "bracket": "\\]"
}

In a Swift raw string, this translates to a simpler form without needing to double up the backslashes:

let jsonRawString = #"""
{
    "bracket": "\\]"
}
"""#

Using Regex Patterns

Working with regex can often lead to a mess of backslashes, making your code hard to read. With Swift’s raw strings, regex patterns become considerably clearer:

let regexString = "\\w"
let regexRawString = #"\w"#

Here the regexString represents the pattern to match any word character, escaped traditionally with two backslashes. The regexRawString, in contrast, uses one backslash made possible by raw strings.

Embedding Regex in JSON Strings

When we embed regex within JSON strings—and then embed those JSON strings within Swift—the escaping can become quite intricate. For regex patterns, each backslash must be escaped once for the regex itself. When placed inside JSON, they must be escaped again, and when that JSON string is placed within Swift, the escaping must be doubled.

For instance, consider a regex that matches any word character, written in Swift as \w. When we place this regex within a JSON string, we need to escape the backslash once for JSON \\w. Now, when we want to embed this JSON within a Swift string, we need to escape each backslash again, resulting in a sequence of double backslashes that are doubled once more for the Swift string itself:

let string = """
{
    "data": "{\\"regex\\": \\"\\\\w\\"}"
}
"""

Here in the string, each \\ represents a single backslash in the JSON object, and the \ before each quote " is necessary to escape the quotes within the Swift string literal.

To simplify the handling of such complex strings, Swift introduced raw strings. With raw strings, we still need to escape characters for the JSON, but we don’t need to escape them a second time for Swift. Thus, the equivalent raw string containing the same JSON object would be:

let rawString = #"""
{
    "data": "{\"regex\": \"\\w\"}"
}
"""#

With the rawString, there is only one level of escaping required for the JSON syntax, as raw strings allow us to include backslashes and quotes without additional Swift-level escaping. The outermost #""" and """# denote a raw string where the usual escaping rules are relaxed. This makes the inclusion of complex strings within Swift code far more readable and easier to manage.

Conclusion

Swift’s raw strings alleviate the complexity commonly associated with including special characters in string literals. They offer a way to write clear and concise string literals, particularly useful when dealing with regex patterns or nested JSON strings. Next time you’re faced with a tangle of backslashes, remember that raw strings could be your path to cleaner, more maintainable code. Whether you are a seasoned Swift developer or just starting, raw strings are a powerful tool to add to your code-writing arsenal.

Escaping with Backslashes#

Embracing Convenience with Swift’s Raw Strings#

Handling JSON String Literals#

Special Characters in JSON and Swift#

Using Regex Patterns#

Embedding Regex in JSON Strings#

Conclusion#