Remember too that in Swift the operator is decoupled from its implementation. Plenty of people are using && for things like constraint or predicate DSLs, where it doesn't short-circuit. Of course, a non-associative version of && would be quite surprising, so even a custom implementation probably shouldn't rely on the left-associativity.
There's one other reason to prefer this way, though, and that's complexity in the AST. Recall that the RHS of the standard && (and ||, and ??) is an auto-closure—Swift's way to avoid the eager evaluation of the argument. Right-associativity would result in heavily-nested autoclosures, and even though they'll all be flattened as part of compilation, the AST representation still has to model them that way. So purely from a compiler-implementation perspective left-associativity has a small edge. I think you're right that we should have picked right-associativity anyway, but at this point I'm not sure it's worth changing it. Jordan > On Feb 17, 2017, at 01:03, Saagar Jha via swift-users <swift-users@swift.org> > wrote: > > Left associativity is most likely just a holdover from the C family–not > conforming with it would break expectations for programmers coming from these > languages. And as you mentioned, the compiler will short-circuit the > condition and stop evaluating as soon as it encounters a false condition, so > there’s no measurable benefit. > > Saagar Jha > >> On Feb 17, 2017, at 12:54 AM, rintaro ishizaki via swift-users >> <swift-users@swift.org <mailto:swift-users@swift.org>> wrote: >> >> Hello all, >> >> Why the associativity of Logical{Conjunction,Disjunction}Precedence is >> "left"? >> >> If you write: A && B && C, it's grouped as (A && B) && C. >> This means that the && function is always called twice: (&&)((&&)(A, B), C). >> I feel "right" associativity is more natural: (&&)(A, (&&)(B, C)), >> because the && function is called only once if A is false. >> >> I know that redundant && calls are optimized away in most cases. >> I also know C and C++ standard says: "The && operator groups left-to-right", >> and most programming languages follow that. >> >> But why not "right" associativity? >> What is the difference between logical operators and ?? operator that has >> "right" associativity? >> >> _______________________________________________ >> swift-users mailing list >> swift-users@swift.org <mailto:swift-users@swift.org> >> https://lists.swift.org/mailman/listinfo/swift-users > > _______________________________________________ > swift-users mailing list > swift-users@swift.org > https://lists.swift.org/mailman/listinfo/swift-users
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