After calling clear() on a std.array.Appender, formattedWrite() using that appender fails silently. Calling the appender's put() method once after a clear() is a workaround. Tested on DMD 2.062.

Example:
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import std.stdio, std.array, std.format, std.string;

void main()
{	
	// FIRST EXAMPLE: use only put().
	auto a = appender!string;
	a.put( format("%d", 1) );
	writeln(a.data);
	a.clear();
	// put() after clear() is OK.
	a.put( format("%d", 2) );
	writeln(a.data);
	assert(a.data == "2");

	// SECOND EXAMPLE: use only formattedWrite().
	auto b = appender!string;
	b.reserve(128);
	formattedWrite(b, "%d", 1);
	writeln(b.data);
	assert(b.data == "1");
	b.clear();
	// formattedWrite() after clear() does not work.
	formattedWrite(b, "%d", 2); // <-- FAILS SILENTLY
	writeln(b.data); // "" (writes empty string)
	assert(b.data == ""); // this should not pass, but it does.
	// You have to call put() on appender before formattedWrite() works again.
	b.put("");
	formattedWrite(b, "%d", 3);
	writeln(b.data);
	assert(b.data == "3");
}
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