如何将C Enum转换为Rust Enum并确定大小

Question

C中的枚举定义如下：

    enum {
        VIRTUALIZATION_NONE = 0,

        VIRTUALIZATION_VM_FIRST,
        VIRTUALIZATION_KVM = VIRTUALIZATION_VM_FIRST,
        VIRTUALIZATION_AMAZON,
        VIRTUALIZATION_QEMU,
        VIRTUALIZATION_BOCHS,
        VIRTUALIZATION_XEN,
        VIRTUALIZATION_UML,
        VIRTUALIZATION_VMWARE,
        VIRTUALIZATION_ORACLE,
        VIRTUALIZATION_MICROSOFT,
        VIRTUALIZATION_ZVM,
        VIRTUALIZATION_PARALLELS,
        VIRTUALIZATION_BHYVE,
        VIRTUALIZATION_QNX,
        VIRTUALIZATION_ACRN,
        VIRTUALIZATION_POWERVM,
        VIRTUALIZATION_VM_OTHER,
        VIRTUALIZATION_VM_LAST = VIRTUALIZATION_VM_OTHER,

        VIRTUALIZATION_CONTAINER_FIRST,
        VIRTUALIZATION_SYSTEMD_NSPAWN = VIRTUALIZATION_CONTAINER_FIRST,
        VIRTUALIZATION_LXC_LIBVIRT,
        VIRTUALIZATION_LXC,
        VIRTUALIZATION_OPENVZ,
        VIRTUALIZATION_DOCKER,
        VIRTUALIZATION_PODMAN,
        VIRTUALIZATION_RKT,
        VIRTUALIZATION_WSL,
        VIRTUALIZATION_PROOT,
        VIRTUALIZATION_POUCH,
        VIRTUALIZATION_CONTAINER_OTHER,
        VIRTUALIZATION_CONTAINER_LAST = VIRTUALIZATION_CONTAINER_OTHER,

        _VIRTUALIZATION_MAX,
        _VIRTUALIZATION_INVALID = -EINVAL,
};

如何将其转换为Rust并调整枚举值的大小？因为我发现铁锈似乎无法做出比判断更大或更平等的判断。

Answer 1

为了实现这一点，您需要使用：

values

• Implement constants

• PartialEq
• 标记和PartialOrd性状

标签值

锈菌枚举可以具有标记值，如：

enum Virtualization {
        VirtualizationNone = 0,
        VirtualizationVMFirst = 1,
        VirtualizationAmazon = 2,
        VirtualizationQEMU = 3,
        ...
        VirtualizationInvalid = -22
}

实现常量

VIRTUALIZATION_KVM = VIRTUALIZATION_VM_FIRST这样的变体会出现问题，就像锈蚀一样，两个枚举变体不能具有相同的标记值。

error[E0081]: discriminant value `1` already exists
 --> src/main.rs:5:22
  |
4 |     VirtualizationVMFirst = 1,
  |                             - first use of `1`
5 |     VirtualizationKVM = 1,
  |                         ^ enum already has `1`

为了解决这个问题，可以对重复值使用impl常量：

#[allow(non_upper_case_globals)]
impl Virtualization {
    pub const VirtualizationKVM: Self = Self::VirtualizationVMFirst;
    pub const VirtualizationVMLast: Self = Self::VirtualizationVMOther;
    ...
}

比较性状

最后，为了比较标记的锈蚀常数，可以导出PartialEq和PartialOrd的实现。

#[derive(PartialEq, PartialOrd)]
enum Virtualization {
    ...
}

现在，您可以比较所有枚举变体和实现常量。例如：

fn main() {
    println!("Virtualization::VirtualizationNone < Virtualization::VirtualizationVMFirst {}", (Virtualization::VirtualizationNone < Virtualization::VirtualizationVMFirst));
    println!("Virtualization::VirtualizationNone > Virtualization::VirtualizationVMFirst {}", (Virtualization::VirtualizationNone > Virtualization::VirtualizationVMFirst));
}

// Virtualization::VirtualizationNone < Virtualization::VirtualizationVMFirst true
// Virtualization::VirtualizationNone > Virtualization::VirtualizationVMFirst false