> On Mar 24, 2017, at 3:57 PM, Peter Dillinger via swift-evolution
> <[email protected]> wrote:
>
> I recently criticized Swift 3 for allowing many expressions with no side
> effects as statements, in this blog post:
> https://blogs.synopsys.com/software-integrity/2017/03/24/swift-programming-language-design-part-2/
> (search for "that expression"). I've seen some related discussion such as
> "Make non-void functions @warn_unused_result by default", but not quite this.
>
> For emphasis, let me include a real example (from open-source software,
> simplified) of defective JavaScript code that happens to be legal Swift as
> well:
>
> var html = "<table class='modification'>" +
> "<tbody>" +
> trs
> "</tbody>" +
> "</table>";
>
> DEFECT SPOILER: (There is a
> missing '+')
>
> Part of my argument is that people commonly ignore compiler warnings. We see
> lots of defective code that would be (or is) caught by compiler warnings but
> people don't pay attention.
>
> I have not formulated this into a detailed proposal, but I suspect that
> because of Swift's pervasive overloading, implicit constructor calls, etc.,
> it would involve introducing a new @error_unused_result annotation and using
> that in many places in the standard library. I also suggest that user
> overloads of traditionally non-side-effecting operators, as well as
> non-mutating struct methods, be @error_unused_result by default, or perhaps
> by mandate. Our experience also suggests this @error_unused_result feature
> could also be useful for ordinary methods of classes, as we find a number of
> defects where a method call is expecting a side effect but there is none,
> because the method is only useful for its return value.
>
> If you would like to see more defect examples from open-source software
> (other languages for the moment), I should be able to dig up some more.
If I copy/paste your code (and add a definition for “trs”), Swift already gives
a warning:
let trs = "trs"
var html = "<table class='modification'>" +
"<tbody>" +
trs
"</tbody>" + // Warning: Result of operator '+' is unused
"</table>";
What version of Swift are you using? IIRC, it didn’t start doing that until
Swift 3.
- Dave Sweeris
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