A slice of a string.
- Xcode 9.0+
- Swift Standard Library
When you create a slice of a string, a
Substring instance is the result. Operating on substrings is fast and efficient because a substring shares its storage with the original string. The
Substring type presents the same interface as
String, so you can avoid or defer any copying of the string’s contents.
The following example creates a
greeting string, and then finds the substring of the first sentence:
You can perform many string operations on a substring. Here, we find the length of the first sentence and create an uppercase version.
Converting a Substring to a String
This example defines a
raw string with some unstructured data, and then uses the string’s
prefix(while:) method to create a substring of the numeric prefix:
When you need to store a substring or pass it to a function that requires a
String instance, you can convert it to a
String by using the
String(_:) initializer. Calling this initializer copies the contents of the substring to a new string.
Alternatively, you can convert the function that takes a
String to one that is generic over the
String protocol. The following code declares a generic version of the
You can call this generic function with an instance of either