如何将 bindgen 生成的 C 风格枚举转换为另一个枚举?
How do I convert a C-style enum generated by bindgen to another enum?
我在 Rust 中为 C 库创建绑定,Bindgen 生成的枚举如下:
// Rust
#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
pub enum rmw_qos_history_policy_t {
RMW_QOS_POLICY_HISTORY_SYSTEM_DEFAULT = 0,
RMW_QOS_POLICY_HISTORY_KEEP_LAST = 1,
RMW_QOS_POLICY_HISTORY_KEEP_ALL = 2,
RMW_QOS_POLICY_HISTORY_UNKNOWN = 3,
}
我需要将它们转换为:
// Rust
pub enum QoSHistoryPolicy {
SystemDefault = 0,
KeepLast = 1,
KeepAll = 2,
Unknown = 3,
}
从该 C 库导入常量值时:
// C library
const rmw_qos_history_policy_t some_value_from_C = RMW_QOS_POLICY_HISTORY_SYSTEM_DEFAULT;
我想做这样的事情:
let some_value: QoSHistoryPolicy = some_value_from_C;
我该怎么做?
它看起来很适合 QoSHistoryPolicy
From
trait。
impl From<rmw_qos_history_policy_t> for QoSHistoryPolicy {
fn from(raw: rmw_qos_history_policy_t) -> Self {
match raw {
rmw_qos_history_policy_t::RMW_QOS_POLICY_HISTORY_SYSTEM_DEFAULT => QoSHistoryPolicy::SystemDefault,
rmw_qos_history_policy_t::RMW_QOS_POLICY_HISTORY_KEEP_LAST => QoSHistoryPolicy::KeepLast,
rmw_qos_history_policy_t::RMW_QOS_POLICY_HISTORY_KEEP_ALL => QoSHistoryPolicy::KeepAll,
rmw_qos_history_policy_t::RMW_QOS_POLICY_HISTORY_UNKNOWN => QoSHistoryPolicy::Unknown
}
}
}
现在应该可以了
let some_value: QoSHistoryPolicy = some_value_from_C.into();
编译器不检查枚举的 ABI 兼容性,因此不提供在这些类型之间转换值的直接方法。以下是一些可能的解决方案。
1。一对一匹配
尽管会导致详尽的代码,但这是微不足道且安全的。
impl From<rmw_qos_history_policy_t> for QoSHistoryPolicy {
fn from(x: rmw_qos_history_policy_t) -> Self {
use rmw_qos_history_policy_t::*;
match x {
RMW_QOS_POLICY_HISTORY_SYSTEM_DEFAULT => QoSHistoryPolicy::SystemDefault,
RMW_QOS_POLICY_HISTORY_KEEP_LAST => QoSHistoryPolicy::KeepLast,
RMW_QOS_POLICY_HISTORY_KEEP_ALL => QoSHistoryPolicy::KeepAll,
RMW_QOS_POLICY_HISTORY_UNKNOWN => QoSHistoryPolicy::Unknown,
}
}
}
2。铸造 + FromPrimitive
Rust 允许您使用 as
运算符将无字段枚举转换为整数类型。然而,相反的转换并不总是安全的。使用 num
箱子导出 FromPrimitive
以获得丢失的部分。
#[derive(FromPrimitive)]
pub enum QoSHistoryPolicy { ... }
impl From<rmw_qos_history_policy_t> for QoSHistoryPolicy {
fn from(x: rmw_qos_history_policy_t) -> Self {
FromPrimitive::from_u32(x as _).expect("1:1 enum variant matching, all good")
}
}
3。需要枚举?
如果您只想对低级绑定进行抽象,则可能不需要新的枚举类型。
#[repr(transparent)]
pub struct QoSHistoryPolicy(rmw_qos_history_policy_t);
上面的类型包含相同的信息和二进制表示,但可以公开封装的 API。从低级类型到高级类型的转换变得微不足道。主要的缺点是你失去了与其变体的模式匹配。
4。你一个人
当绝对确定两个枚举的二进制表示形式相同时,您可以transmute
它们之间。编译器不会在这里帮助你,这远非推荐。
unsafe {
let policy: QoSHistoryPolicy = std::mem::transmute(val);
}
另请参阅:
- How do I match enum values with an integer?
我在 Rust 中为 C 库创建绑定,Bindgen 生成的枚举如下:
// Rust
#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
pub enum rmw_qos_history_policy_t {
RMW_QOS_POLICY_HISTORY_SYSTEM_DEFAULT = 0,
RMW_QOS_POLICY_HISTORY_KEEP_LAST = 1,
RMW_QOS_POLICY_HISTORY_KEEP_ALL = 2,
RMW_QOS_POLICY_HISTORY_UNKNOWN = 3,
}
我需要将它们转换为:
// Rust
pub enum QoSHistoryPolicy {
SystemDefault = 0,
KeepLast = 1,
KeepAll = 2,
Unknown = 3,
}
从该 C 库导入常量值时:
// C library
const rmw_qos_history_policy_t some_value_from_C = RMW_QOS_POLICY_HISTORY_SYSTEM_DEFAULT;
我想做这样的事情:
let some_value: QoSHistoryPolicy = some_value_from_C;
我该怎么做?
它看起来很适合 QoSHistoryPolicy
From
trait。
impl From<rmw_qos_history_policy_t> for QoSHistoryPolicy {
fn from(raw: rmw_qos_history_policy_t) -> Self {
match raw {
rmw_qos_history_policy_t::RMW_QOS_POLICY_HISTORY_SYSTEM_DEFAULT => QoSHistoryPolicy::SystemDefault,
rmw_qos_history_policy_t::RMW_QOS_POLICY_HISTORY_KEEP_LAST => QoSHistoryPolicy::KeepLast,
rmw_qos_history_policy_t::RMW_QOS_POLICY_HISTORY_KEEP_ALL => QoSHistoryPolicy::KeepAll,
rmw_qos_history_policy_t::RMW_QOS_POLICY_HISTORY_UNKNOWN => QoSHistoryPolicy::Unknown
}
}
}
现在应该可以了
let some_value: QoSHistoryPolicy = some_value_from_C.into();
编译器不检查枚举的 ABI 兼容性,因此不提供在这些类型之间转换值的直接方法。以下是一些可能的解决方案。
1。一对一匹配
尽管会导致详尽的代码,但这是微不足道且安全的。
impl From<rmw_qos_history_policy_t> for QoSHistoryPolicy {
fn from(x: rmw_qos_history_policy_t) -> Self {
use rmw_qos_history_policy_t::*;
match x {
RMW_QOS_POLICY_HISTORY_SYSTEM_DEFAULT => QoSHistoryPolicy::SystemDefault,
RMW_QOS_POLICY_HISTORY_KEEP_LAST => QoSHistoryPolicy::KeepLast,
RMW_QOS_POLICY_HISTORY_KEEP_ALL => QoSHistoryPolicy::KeepAll,
RMW_QOS_POLICY_HISTORY_UNKNOWN => QoSHistoryPolicy::Unknown,
}
}
}
2。铸造 + FromPrimitive
Rust 允许您使用 as
运算符将无字段枚举转换为整数类型。然而,相反的转换并不总是安全的。使用 num
箱子导出 FromPrimitive
以获得丢失的部分。
#[derive(FromPrimitive)]
pub enum QoSHistoryPolicy { ... }
impl From<rmw_qos_history_policy_t> for QoSHistoryPolicy {
fn from(x: rmw_qos_history_policy_t) -> Self {
FromPrimitive::from_u32(x as _).expect("1:1 enum variant matching, all good")
}
}
3。需要枚举?
如果您只想对低级绑定进行抽象,则可能不需要新的枚举类型。
#[repr(transparent)]
pub struct QoSHistoryPolicy(rmw_qos_history_policy_t);
上面的类型包含相同的信息和二进制表示,但可以公开封装的 API。从低级类型到高级类型的转换变得微不足道。主要的缺点是你失去了与其变体的模式匹配。
4。你一个人
当绝对确定两个枚举的二进制表示形式相同时,您可以transmute
它们之间。编译器不会在这里帮助你,这远非推荐。
unsafe {
let policy: QoSHistoryPolicy = std::mem::transmute(val);
}
另请参阅:
- How do I match enum values with an integer?