相关疑难解决方法(0)

我有一个涉及宏的编译错误:

<mdo macros>:6:19: 6:50 error: cannot move out of captured outer variable in an `FnMut` closure
<mdo macros>:6 bind ( $ e , move | $ p | mdo ! { $ ( $ t ) * } ) ) ; (
                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
<mdo macros>:1:1: 14:36 note: in expansion of mdo!
<mdo macros>:6:27: 6:50 note: expansion site
<mdo macros>:1:1: 14:36 note: in expansion of mdo!
<mdo macros>:6:27: 6:50 note: expansion site
<mdo macros>:1:1: 14:36 note: in expansion of mdo!
src/parser.rs:30:42: …

我想申请filter一个迭代器,我想出了这个并且它可以工作,但它超级详细:

.filter(|ref my_struct| match my_struct.my_enum { Unknown => false, _ => true })

我宁愿写这样的东西:

.filter(|ref my_struct| my_struct.my_enum != Unknown)

这给了我一个编译错误

binary operation `!=` cannot be applied to type `MyEnum`

有冗长模式匹配的替代方案吗？我寻找一个宏但找不到合适的宏.

编者注:此代码示例来自1.0之前的Rust版本,并且在语法上不是有效的Rust 1.0代码.此代码的更新版本会产生不同的错误,但答案仍包含有价值的信息.

在下列情况下,似乎我们无法测试相等性.为什么是这样？有解决方法吗？(我正在使用Rust 0.11).

trait A: PartialEq {}

#[deriving(PartialEq)]
enum T {Ta, Tb}

impl A for T {}

fn main() {
  assert!(Ta == Ta);
  assert!(Ta != Tb);
  assert!(some_fn(&Ta, &Ta));
  assert!(!some_fn(&Ta, &Tb));
}

fn some_fn(an_a: &A, another_a: &A) -> bool {
    an_a == another_a
// ERROR ^~~~~~~~~~~~ binary operation `==` cannot be applied to type `&A`
}

fn another_fn(an_a: &A + PartialEq, another_a: &A + PartialEq) -> bool {
               // ERROR: ^~~~~~~~~ only the builtin traits can be used as closure …

我想在一个中使用特征对象Vec.在C++中我可以使一个基类Thing从中导出Monster1和Monster2.然后我可以创建一个std::vector<Thing*>.Thing对象必须存储一些数据,例如x : int, y : int,派生类需要添加更多数据.

目前我有类似的东西

struct Level {
    // some stuff here
    pub things: Vec<Box<ThingTrait + 'static>>,
}

struct ThingRecord {
    x: i32,
    y: i32,
}

struct Monster1 {
    thing_record: ThingRecord,
    num_arrows: i32,
}

struct Monster2 {
    thing_record: ThingRecord,
    num_fireballs: i32,
}

我定义了一个ThingTrait与方法get_thing_record(),attack(),make_noise()等,并实现它们的Monster1和Monster2.

我正在尝试检查两个(功能相同)结构的相等性.

#[derive(PartialEq, Debug)]
pub struct TypeA<'a>(&'a str);

#[derive(PartialEq, Debug)]
pub struct TypeB<'a>(&'a str);

impl<'a> TypeA<'a> {
    pub fn new(n: &str) -> TypeA {
        TypeA(n)
    }
}

impl<'a> TypeB<'a> {
    pub fn new(n: &str) -> TypeB {
        TypeB(n)
    }
}

fn main() {
    assert_eq!(TypeA::new("A"), TypeB::new("A"));
}

它返回错误:

error[E0308]: mismatched types
  --> src/main.rs:20:5
   |
20 |     assert_eq!(TypeA::new("A"), TypeB::new("A"));
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected struct `TypeA`, found struct `TypeB`
   |
   = note: expected type `TypeA<'_>`
              found type `TypeB<'_>`
   = note: this error originates in a …