我正在尝试为Expat XML解析器实现Rust包装器 . 我包装了start_element,end_element回调,它们在简单的情况下工作正常(例如,只计算XML元素),如下所示:
struct Expat {
parser: expat::XML_Parser
}
type StartHandler = @fn(tag: &str, attrs: &[~str]);
type EndHandler = @fn(tag: &str);
type TextHandler = @fn(text: &str);
struct Handlers {
start_handler: StartHandler,
end_handler: EndHandler,
text_handler: TextHandler
}
impl Expat {
pub fn handlers(&self, start_handler: StartHandler, end_handler: EndHandler, text_handler: TextHandler) {
let handlers = @Handlers {
start_handler: start_handler,
end_handler: end_handler,
text_handler: text_handler
};
// How to do this properly?
unsafe { cast::bump_box_refcount(handlers) };
expat::XML_SetUserData(self.parser, unsafe { cast::transmute(&*handlers) });
}
我可以将简单的托管闭包传递给处理程序()并让它们更新@mut uint值 .
现在我想在回调中维护当前的XPath并遇到问题:
let mut xpath: ~[~str] = ~[];
let xpath_start_handler: @fn(&str, &[~str]) = |tag: &str, _attrs: &[~str]| {
vec::push(&xpath, tag.to_owned());
println(fmt!(" start: %?", xpath));
};
let xpath_end_handler: @fn(&str) = |tag: &str| {
println(fmt!(" end: %?", xpath));
let top = vec::pop(&xpath);
if top != tag.to_owned() {
fail!(fmt!("expected end tag: %s, received end tag: %s", top, tag));
}
};
let xpath_text_handler: @fn(&str) = |_text: &str| {
};
expat.handlers(xpath_start_handler, xpath_end_handler, xpath_text_handler);
编译器说,唯一的向量xpath被移动到xpath_start_handler闭包中,无法在xpath_end_closure中访问 .
所以我的问题是在多个托管闭包中保持可变状态的最佳方法是什么?
1 回答
应该管理共享框,而不是唯一框:
此外,可变的唯一框与可变管理框的工作方式略有不同 .