[Issue 15882] writeln on a bad dstring triggering assert(0) in std.utf.toUTF8

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=15882

--- Comment #2 from erikas.aubade at gmail.com ---
An assert failure is not considered a recoverable error; as i understand it
should be indicative of a critical flaw in logic, not an indication of bad
input.

It's also inconsistent with the way D treats bad unicode elsewhere. For
instance, if you put that bad string in a struct, it will wrilen with no error
and simply display as a hex-literal. In the functions that decode utf8 to
utf32, bad unicode will issue a recoverable exception.

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