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import std.range: put;
import std.array: appender;
import std.format: formattedWrite;
struct Foo
{
void toString(Writer)(ref Writer writer)
{
put(writer, "Foo");
}
}
void main()
{
auto buffer = appender!string;
Foo foo;
formattedWrite(buffer, "%s", foo);
assert(buffer[] == "Foo");
}