Psych::Emitter.new

static VALUE initialize(int argc, VALUE *argv, VALUE self)
{
    yaml_emitter_t * emitter;
    VALUE io, options;
    VALUE line_width;
    VALUE indent;
    VALUE canonical;

    TypedData_Get_Struct(self, yaml_emitter_t, &psych_emitter_type, emitter);

    if (rb_scan_args(argc, argv, "11", &io, &options) == 2) {
        line_width = rb_funcall(options, id_line_width, 0);
        indent     = rb_funcall(options, id_indentation, 0);
        canonical  = rb_funcall(options, id_canonical, 0);

        yaml_emitter_set_width(emitter, NUM2INT(line_width));
        yaml_emitter_set_indent(emitter, NUM2INT(indent));
        yaml_emitter_set_canonical(emitter, Qtrue == canonical ? 1 : 0);
    }

    rb_ivar_set(self, id_io, io);
    yaml_emitter_set_output(emitter, writer, (void *)self);

    return self;
}