objective c - Why can't LLDB evaluate this expression?

Question

Neither one of these statements can be processed by LLDB... why is it unable to come up with the NSString result and print it out

expr -o -- [NSString stringWithFormat:@"%@", @"Wow this doesnt work??"]

po [NSString stringWithFormat:@"%@", @"Wow this doesnt work??"]

Answer 1

It seems that the expression command in lldb can generally not evaluate functions with variable argument lists. It fails even with a simple C function:

int foo(char *msg, ...)
{
    return 17;
}

(lldb) expr foo("bar")
(int) $2 = 17

(lldb) expr foo("bar", 2)
error: no matching function for call to 'foo'
note: candidate function not viable: requires 1 argument, but 2 were provided
error: 1 errors parsing expression

So this looks like a bug (or non-feature) in lldb.