Function tao_of_rust::ch12::reflect::any_function

pub fn any_function()

使用Any进行反射

Basic usage: 使用is函数进行类型判断

use std::any::{Any, TypeId};
 
enum E { H, He, Li}
 
struct S { x: u8, y: u8, z: u16 }
 
fn main() {   
    let v1 = 0xc0ffee_u32;
    let v2 = E::He;
    let v3 = S { x: 0xde, y: 0xad, z: 0xbeef };
    let v4 = "rust";
    let mut a: &Any; // trait object
   a = &v1;
   assert!(a.is::<u32>());
   // TypeId { t: 12849923012446332737 }
   println!("{:?}", TypeId::of::<u32>());   
   a = &v2;
   assert!(a.is::<E>());
   // TypeId { t: 15527215023668350898 }
   println!("{:?}", TypeId::of::<E>());   
   a = &v3;
   assert!(a.is::<S>());
   // TypeId { t: 17868507538031848664 }
   println!("{:?}", TypeId::of::<S>());   
   a = &v4;
   assert!(a.is::<&str>());
   // TypeId { t: 1229646359891580772 }
   println!("{:?}", TypeId::of::<&str>());   
}

Basic usage: 使用downcase_ref转换到具体类型

use std::any::Any;
#[derive(Debug)]
enum E { H, He, Li}
struct S { x: u8, y: u8, z: u16 }
fn print_any(a: &Any) {
    if let Some(v) = a.downcast_ref::<u32>() {
        println!("u32 {:x}", v);
    } else if let Some(v) = a.downcast_ref::<E>() {
        println!("enum E {:?}", v);
   } else if let Some(v) = a.downcast_ref::<S>() {
       println!("struct S {:x} {:x} {:x}", v.x, v.y, v.z);
   } else {
       println!("else!");
   }
}
fn main() {
   print_any(& 0xc0ffee_u32);                       
   print_any(& E::He);                             
   print_any(& S{ x: 0xde, y: 0xad, z: 0xbeef }); 
   print_any(& "rust");                           
   print_any(& "hoge");                           
}

Basic usage: 使用Box

use std::any::Any;
fn print_if_string(value: Box<Any>) {
    if let Ok(string) = value.downcast::<String>() {
        println!("String (length {}): {}", string.len(), string);
    }else{
        println!("Not String")
    }
}
fn main() {
   let my_string = "Hello World".to_string();
   print_if_string(Box::new(my_string));
   print_if_string(Box::new(0i8));
}

Basic usage: 非静态生命周期的类型未实现Any

use std::any::Any;
struct UnStatic<'a> { x: &'a i32 }
fn main() {
    let a = 42;
    let v = UnStatic { x: &a };
    let mut any: &Any;
    //any = &v;  // Compile Error!
}

Basic usage: 使用静态生命周期类型的值创建UnStatic实例

正常编译

use std::any::Any;
struct UnStatic<'a> { x: &'a i32 }
static ANSWER: i32 = 42;
fn main() {
    let v = UnStatic { x: &ANSWER };
    let mut a: &Any;
    a = &v;
    assert!(a.is::<UnStatic>());
}