[Issue 4558] New: To spot a possible bug in code that doesn't change a value

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=4558

           Summary: To spot a possible bug in code that doesn't change a
                    value
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Keywords: diagnostic
          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 2010-08-01 14:20:33 PDT ---
This is a semantically wrong D2 program, the programmer has used a "&=" instead
of "|=" to build a flag result:


enum Flags { NONE   = 0b00,
             FIRST  = 0b01,
             SECOND = 0b10
}
Flags foo(int x) {
    Flags result = Flags.NONE;
    if (x < 10)
        result |= Flags.FIRST;
    else
        result &= Flags.SECOND; // line 10
    return result;
}
void main() {}


The D compiler can find this problem in the code at line 10 because in that
program the variable "result" is certantly zero after the assignment with
Flags.SECOND, so it's an error or it's useless code.

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