Downsizes the string to a length of
n characters (utf code units).
void downsize (
const size_t n
) pure nothrow @nogc scope @safe;
n is smaller than the current string length, the current value is shortened to its first
n character, removing the characters beyond the nth.
n is greater or equal than the current string length, the nothing happend.
BasicString!char str = "123"; str
.downsize(5); assert(str == "123"); str .downsize(2); assert(str == "12");