{"id":36765,"date":"2022-08-12T16:39:15","date_gmt":"2022-08-12T20:39:15","guid":{"rendered":"https:\/\/mjtsai.com\/blog\/?p=36765"},"modified":"2022-08-12T16:39:15","modified_gmt":"2022-08-12T20:39:15","slug":"swift-pitch-borrow-and-take-parameter-ownership-modifiers","status":"publish","type":"post","link":"https:\/\/mjtsai.com\/blog\/2022\/08\/12\/swift-pitch-borrow-and-take-parameter-ownership-modifiers\/","title":{"rendered":"Swift Pitch: “borrow” and “take” Parameter Ownership Modifiers"},"content":{"rendered":"

Joe Groff<\/a>:<\/p>\n

\n

We propose new borrow<\/code> and take<\/code> parameter modifiers to allow developers to explicitly choose the ownership convention that a function uses to receive immutable parameters. This allows for fine-tuning of performance by reducing the number of ARC calls or copies needed to call a function, and provides a necessary prerequisite feature for move-only types to specify whether a function consumes a move-only value or not.<\/p>\n

[…]<\/p>\n

Looking to the future, as part of our ongoing project to add ownership to Swift<\/a>, we will eventually have move-only values and types. Since move-only types do not have the ability to be copied, the distinction between the two conventions becomes an important part of the API contract: functions that borrow<\/em> move-only values make temporary use of the value and leave it valid for further use, like reading from a file handle, whereas functions that take<\/em> a move-only value consume it and prevent its further use, like closing a file handle. Relying on implicit selection of the parameter convention will not suffice for these types.<\/p>\n<\/blockquote>\n\n

Previously:<\/p>\n