On Tuesday, 21 November 2017 at 19:05:21 UTC, Jonathan M Davis
wrote:
Well, the assertion is going to throw an AssertError, which
takes a string for its message. It doesn't copy the contents of
the string. It's just taking a slice just like whenever you
pass a string to any other function. So, it refers to the same
memory as what's passed in. So, if what it's passed is a string
that refers to memory on the stack, then when it goes to print
the message, it's going to be garbage, because the stack was
unwound, and the static array is gone.
Honestly, I'd argue that it's a bug that it allows you provide
a message as a char[] instead of immutable(char)[]. It seems
that the compiler is implicitly converting char[] to
immutable(char)[] in this case, which is very bad. It would
matter less if you were giving the assertion a char[] that
referred to memory on the heap, but it still shouldn't be
allowed.
You really should be giving assertions a value that is an
actual string that lives on the heap when providing a message,
not a char[], and definitely not a char[] that's a slice of a
static array.
- Jonathan M Davis
Right. So a literal would work, because it's in the .data
segment, or inlined. Basically, only strings from the heap, or
that are compiled into the code are valid for assert messages.
What kind of behavior would an assert from stdc have (id,
betterC)?
