# appendInterpolation(_:specifier:) Appends a type, convertible to a string with a format specifier, to a string interpolation. ``` mutating func appendInterpolation(_ value: T, specifier: String) where T : _FormatSpecifiable ``` ## Parameters `value` The value to append. `specifier` A format specifier to convert `subject` to a string representation, like `%f` for a , or `%x` to create a hexidecimal representation of a . For a list of available specifier strings, see [String Format Specifers](https://developer.apple.com/library/archive/documentation/CoreFoundation/Conceptual/CFStrings/formatSpecifiers.html#//apple_ref/doc/uid/TP40004265). ## Discussion Don’t call this method directly; it’s used by the compiler when interpreting string interpolations. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)