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Rust-langRust-langPosted Apr 5, 2013 12:54 UTC (Fri) by HelloWorld (guest, #56129)In reply to: Rust-lang by dgm Parent article: Mozilla and Samsung building a new browser engine
It is trivial to add a warning for that. Just check if a local variable is bound to a value of type ().
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Rust-lang Posted Apr 5, 2013 17:01 UTC (Fri) by jimparis (subscriber, #38647) [Link]
A runtime warning? It's hardly trivial at compile time when the compiler might not even know if a branch can be taken.
Rust-lang Posted Apr 5, 2013 22:18 UTC (Fri) by HelloWorld (guest, #56129) [Link]
> A runtime warning? It's hardly trivial at compile time when the compiler might not even know if a branch can be taken.
It doesn't matter whether the branch can be taken, the values of both branches are of type (), and it doesn't make sense to store a value of that type in a variable.
Rust-lang Posted Apr 5, 2013 22:47 UTC (Fri) by jimparis (subscriber, #38647) [Link]
> It doesn't matter whether the branch can be taken, the values of both branches are of type ()
So imagine a case where both branches are different. Or where the conditional is deep inside a function before the return value finally gets to the assignment. If having a conditional return type () makes sense in some cases and not others, then you can't trivially warn about it.
Rust-lang Posted Apr 6, 2013 0:26 UTC (Sat) by HelloWorld (guest, #56129) [Link]
> So imagine a case where both branches are different.
That's a type error in itself in most cases. In order for such code to typecheck, the branches' types must have a common supertype. As far as I can see, Rust allows only interfaces to form hierarchies, and I don't know if it's even possible for () to implement interfaces. But even if it is, this situation is going to be so rare that it's not worth losing any sleep over it.
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