Function diff(_:_:format:)
public func diff<T>(_ lhs: T, _ rhs: T, format: DiffFormat = .default) -> String? Detects differences between two given values by comparing their mirrors and optionally returns a formatted string describing it.
This can be a great tool to use for building debug tools for applications and libraries. For
example, this library uses diff(_:_:format:) to implement
XCTAssertNoDifference(_:_:_:file:line:), which asserts that two values are equal, and
if they are not the failure message is a nicely formatted diff showing exactly what part of the
values are not equal.
Further, the
Composable Architecture uses
diff(_:_:format:) in a couple different ways:
-
It is used to implement a tool that prints changes to application state over time as diffs between the previous state and the current state whenever an action is sent to the store.
-
It is also used in a testing tool so that when one fails to assert for how state may have changed after sending an action, it can display a concise message showing the exact difference in state.
Parameters
| Name | Type | Description |
|---|---|---|
| lhs | T |
An expression of type |
| rhs | T |
A second expression of type |
| format | DiffFormat |
A format to use for the diff. By default it uses ASCII characters typically associated with the "diff" format: "-" for removals, "+" for additions, and " " for unchanged lines. |
Returns
A string describing any difference detected between values, or nil if no difference is detected.