Freestanding Macro that doesn't return an expression

I was trying to implement Assign if different using freestanding macro and I did succeed but kind of cheating using a closure because the freestanding macro is expected to return and expression.

#assign(b, to: a, if: !=) for example is expanded to:

    if a != b {
        a = b

Is this the only way to currently do this? Any plans to lift this restriction with another kind of freestanding macro?


This is the only way to do this today. The early pitches for declaration macros had "code item" macros that could do this, and there's a partial implementation of the feature in the compiler behind an experimental feature flag (CodeItemMacros), but nobody has followed through with pitch/proposal/complete implementation. Personally, I haven't seen that many use cases for code-item macros vs. the other kinds, so I haven't looked into them further.




I have a use case for this kind of feature that might be valuable.

It's not possible to possible to wrap os log calls because OSLogMessage cannot be initiliazed from a String variable, it forces us to duplicate log lines to both log into Unified logging system and to Crashlytics for example.

I would like to use a macro to expand the boilerplate code that perform those 2 calls. It seems that only CodeItemMacro can achieve this but I might be wrong...

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I created a macro for this exact same use case, and ended up using the same immediately-executed closure strategy described in the original post here, in order to consolidate the two expressions down to a single one.

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