[Issue 8757] New: Require parenthesization of ternary operator when compounded

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=8757

           Summary: Require parenthesization of ternary operator when
                    compounded
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: bearophile_hugs at eml.cc


--- Comment #0 from bearophile_hugs at eml.cc 2012-10-04 09:47:28 PDT ---
In past we have discussed in the D newsgroups about the bug-prone precedence of
the ?: operator. Analysis of shared code repositories (and articles about
static code analysis) shows that this is a common source of bugs. So I suggest
to look for wasy to avoid/reduce such bugs in D code.

One of the possible ideas is (this is a small breaking change): when the ?: is
included in a larger expression, require parentheses around it.

auto x1 = y1 ? z1 : w1; // OK
auto x2 = x0 + (y1 ? z1 : w1); // OK
auto x3 = (x0 + y1) ? z1 : w1; // OK
auto x4 = x0 + y1 ? z1 : w1; // Compilation error
auto x5 = y1 ? z1 : (y2 ? z2 : w2); // OK
auto x6 = y1 ? z1 : y2 ? z2 : w2; // Compilation error


In theory this increases the number of parentheses a little, but in practice in
many similar situations I already put those parentheses, for readability and to
avoid some of my mistakes.

Ideas for other solutions are welcome.

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