http://d.puremagic.com/issues/show_bug.cgi?id=3882
Summary: Unused result of pure functions Product: D Version: 2.040 Platform: All OS/Version: All Status: NEW Severity: enhancement Priority: P2 Component: DMD AssignedTo: nob...@puremagic.com ReportedBy: bearophile_h...@eml.cc --- Comment #0 from bearophile_h...@eml.cc 2010-03-05 10:31:12 PST --- The following small program: void main() { int x = 5; x + 3; } Currently produces the compile error: Error: + has no effect in expression (x + 3) because that's often a small bug in the program. Equally, a pure function has no side effects, so its only purpose is to return a value. So the compiler can issue a warning or error if its return value is not used. This can help avoid some small bugs. This predecessor() function computes the predecessor of its input argument, its result is always nonnegative: pure int predecessor(int x) { if (x <= 0) throw new Exception(""); return x - 1; } void main() { predecessor(5); // warning or error } In theory a pure function can be used just for the exceptions it throws, but I think this is a quite uncommon usage. A "pure nothrow" function can't even have this uncommon purpose, so this can produce a compile error: pure nothrow int predecessor(int x) { return x - 1; } void main() { predecessor(5); // error } -------------- In GCC there is a function attribute named "warn_unused_result": http://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html The warn_unused_result attribute causes a warning to be emitted if a caller of the function with this attribute does not use its return value. This is useful for functions where not checking the result is either a security problem or always a bug, such as realloc. Similar attribute can be named like @do_use_result in D2. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------