Use StaticString for Parameter file and function about swift-log HOT 5 CLOSED

I think String is better than StaticString, it should in fact be faster.

• String is exactly 2 words wide, StaticString is 2 words + 1 byte wide (I know, a mistake that's now unfixable with ABI). So passing a StaticString knocks out 3 registers, String only 2
• String is more powerful than StaticString
• String also has an "immortal" representation. So if you create a String that is in fact a static string, it won't allocate and its pointer will go straight into the data section.

@ShivaHuang I would suggest that everybody switch to String instead of StaticString. But do you have a concrete logging backend in mind where you'd need to pass file as a StaticString?

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I'll close this issue.

Thank you @ktoso and @weissi, I learned a lot in this discussion.

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I believe @weissi explored this topic in great depth with specific focus on OSLog so he should be able to answer best here.

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Great point!

I misunderstood the performance and memory usage between String and StaticString. And I agree that String is overall more suitable than StaticString.

The logging backend use StaticString I encounter is CocoaLumberjack.

However, after digging into their code, they also convert the StaticString to String before passing it to the underlay OC code. here
I think I should submit a PR to CocoaLumberjack for that. 😉

BTW, while searching some similar use case in Apple's SDK, I found some functions use StaticString for the same propose. like

• XCTAssertEqual from XCTest
• assertionFailure(_:file:line:) from Swift Standard Library

Will Apple also change their code? 🤣

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@ShivaHuang until Swift 4.2, StaticString was much faster which is why XCTAssertEqual was designed the way it is. Same for assertionFailure etc, now they can’t easily change that because of source/ABI compat.

Also: StaticString should just be 1 word, there’s no reason except that nobody noticed until the ABI was fixed 😬

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