Dangerous undefined value

[nine-fox]

Zig Version

0.14.dev

Steps to Reproduce and Observed Behavior

The following code is valid but extremely dangerous, because val is rubbish value. No any warnning messages.

When myfunc is from 3rd party, how do I know the returned value is valid？

Also, I can not even check val value using == undefined because 0.14 will emit an error.

I would suggest undefined value should not be returned when function marked with ?. At least a warning is needed？

fn myfunc() ?u32 {
return undefined;
}
test "aa" {
if (myfunc()) |val| {
std.debug.print("{}\n", .{val});
}
}

Expected Behavior

emit an error

[andrewrk]

duplicate of #63 (not a bug)

[nektro]

related #211

undefined is not detectable at runtime and using it must be done with caution otherwise you may run into the aptly named undefined behavior. it is up to the programmer to use undefined safely in the cases where the compiler is not able to check it.

[nine-fox]

hi @andrewrk @nektrne thanks for your comments and I know the background to introduce undefined. However, compare to null which is much safer, then whats scenarios should use undefined？

If there are cases to be dangerous, I would think undefined should not be used in production. Make an option to turn undefined on/off？

[nine-fox]

@nektro also in the code above, this case can be detected, bu no error？even a warning is better. Comptime undefined can be detected

[nektro]

undefined is most often used to leave a value uninitialized for later use. for instance:

var buffer: [1024]u8 = undefined;
const slice = foo(&buffer);

happy to discuss more in a Community