Be able to supply values such as "-DBUILD_DATE=21/12/1953” to Swift compiler

Evolution Pitches
9

@johnno1962 I've read the latest draft of your proposal at apple/swift-evolution#917.

I don't like the proposed solution, which treats -DNUMBER=10 as true within an #if NUMBER condition. I think Swift previously had some implicit conversions to Bool but they were removed. Although you could argue that compilation directives are different from normal Swift code.

Could this feature be more like:

  • the special literals such as #file and #line;
  • or the playground literals such as #colorLiteral?

For example, a compiler flag other than -D could be used:

  • either to allow #tolerance and other custom literals;
  • or #userLiteral("tolerance") where only the string argument is user-defined.

The implementation uses strtoll and strtod to validate numeric literals, which won't recognize binary 0b or octal 0o prefixes, or _ underscores used as separators. Should multiline and raw string literals be allowed? Should interpolated string literals be disallowed? Is it possible to inject arbitrary code via the compiler flag?

@jrose Could the package manager's compelling use cases be added to the Motivation section?

The current motivation (to embed information in the binary) might be solved in a different way. For example:

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