Question

Template Toolkit 中是否有打印变量类型的语句？这是为了调试目的。我试图找到类似的东西：

type(my_var)

输出：

scalar

Answer 1

使用 PERL directive。示例：

use downcast_rs::{Downcast, impl_downcast};
use std::sync::{Arc, Mutex};
use std::any::Any;

trait Base: Downcast {}
impl_downcast!(Base);

#[derive(Debug)]
struct Foo {
    /// A `u8` that is owned by this Foo, like a `Box<u8>`
    x: *mut u8
}
impl Foo {
    pub fn new(inner: Box<u8>) -> Self {
        Foo {
            x: Box::into_raw(inner)
        }
    }
    pub fn access(&self) -> u8 {
        unsafe {
            // This is sound, because we 'own' x so only we have access
            *self.x
        }
    }
}
// `x` is 'owned' (like a Box) so we may move it between threads,
// without fearing that it to gets deallocated
unsafe impl Send for Foo {}

impl Base for Foo {}

fn main() {
    let x = Box::new(42);
    // Move x into Foo (no references)
    let foo = Foo::new(x);
    // Create a shareable Foo
    // Notice that `base` is Send & Sync
    let base: Arc<Mutex<dyn Base + Send>> = Arc::new(Mutex::new(foo));
    // Move it to an other thread
    std::thread::spawn(move || {
        // Lock mutex
        let guard = base.lock().unwrap();
        // Coerce to a simple trait object, so we can call trait-methods on it
        let my_base: &dyn Base = &*guard;
        if let Some(foo) = my_base.downcast_ref::<Foo>() {
            println!("{:?} = {}", foo, foo.access());
        } else {
            println!("Not a Foo");
        }
    }).join();
}

如何检查模板工具包中的变量类型？

1 个答案: