SE-0212 — Compiler Version Directive

The review of SE-0212 — Compiler Version Directive begins now and runs through May 7, 2018.

The proposal is available here:

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Ted Kremenek
Review Manager


I see the theoretical benefit of this new directive. Since it’s purely additive, it seems like a reasonable addition.

Is there any specific example that’s been cited where this would be useful in practice (perhaps from the pitch thread)? I can’t think of any real-world use case where I’d need to know more than just the swift version.

Here’s a an example from the wild (PromiseKit):

that could be simplified to:

#if compiler(>=4.2)

And those conditionals will continue to grow more complicate as more language compatibility modes are introduced.


+1 to this proposal.

I think there’s a typo worth mentioning;

It creates an exponential growth in the number of Swift versions for each new compatibility version.

I’m pretty sure it’s quadratic, not exponential. Let N be the number of Swift versions available for compatibility. N is roughly equivalent to the numbers of compiler versions provided. Then, we have:

  • For each compiler version i:
    • For each available language version j <= i:
      Implement compatibility for version j.

Since both loops are bounded by N in size, you have O(N^2) implementations being supported across all compiler versions being provided.

1 Like

You’re correct. I’ve made the change (and fixed other typos) in the proposal.

1 Like

I’m in favor of this but as belatedly noted in the pitch thread we still need to use “4.1.50” (or similar) as the language version for -swift-version 4 in the Swift 4.2 compiler…so that 4.1 compilers can distinguish between Swift 4.1.x and Swift 4.2-in-4-mode! If you need to be compatible with a 4.0 or 4.1 compiler, you have to keep using #if swift a little longer.

@hartbit : Can you incorporate this revision into the proposal? Otherwise, the proposal is going to be accepted as is.

Proposal Accepted

SE-0212 has been accepted, with the following minor amendment mentioned by @jrose:

Thanks for everyone who participated in this review!

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