When do I need placeholder?

[Berhtulf]

This might be a silly question, but when exactly do I have to provide a placeholder? I am looking at the isowords examples and there are all sorts of calls in Clients... sync/async, throwing, returning Void, returning values etc.

But I can't figure out when do I have to add the placeholder. Only time I get some kind of feedback is the fatalError during testing, if a function is called without specifying test dependency version.

Is it possible to provide some guidance in the documentation, XCTUnimplemented initialization or some compile time checks?

[stephencelis]

Generally, unimplemented will try to fail and not use a placeholder. For example, all throwing functions that are overridden using unimplemented will simply throw. For non-throwing versions, a placeholder value can be set to be returned, but can be omitted, in which case the library will attempt to generate a placeholder, or fail with a fatalError.

We mainly support automatic placeholders for Void values and for empty collections: https://github.com/pointfreeco/xctest-dynamic-overlay/blob/main/Sources/XCTestDynamicOverlay/Unimplemented.swift#L547-L553

@iampatbrown Opened a PR to add more defaults, though, which we should maybe revisit: https://github.com/pointfreeco/xctest-dynamic-overlay/pull/25