String copying fails when output from assert

[Adam D. Ruppe]

On Tuesday, 21 November 2017 at 18:49:40 UTC, David  Zhang wrote:
> 	assert(false, chars[0..str.length]);
> }
>
> What am I missing here?

You're escaping a reference to a local variable there. chars[] is 
a pointer to the stack, which is promptly smashed when the assert 
error starts working up the call chain, so by the time it 
actually prints, you have undefined behavior.