这个例子来自core::any
use std::fmt::Debug;
use std::any::Any;
// Logger function for any type that implements Debug.
fn log<T: Any + Debug>(value: &T) {
let value_any = value as &dyn Any;
// try to convert our value to a String. If successful, we want to
// output the String's length as well as its value. If not, it's a
// different type: just print it out unadorned.
match value_any.downcast_ref::<String>() {
Some(as_string) => {
println!("String ({}): {}", as_string.len(), as_string);
}
None => {
println!("{:?}", value);
}
}
}
// This function wants to log its parameter out prior to doing work with it.
fn do_work<T: Any + Debug>(value: &T) {
log(value);
// ...do some other work
}
fn main() {
let my_string = "Hello World".to_string();
do_work(&my_string);
let my_i8: i8 = 100;
do_work(&my_i8);
}
这是我第一次看到+
类型之间的Any + Debug
操作数。我假设它像algebraic types,因此将是Any
类型与Debug
类型;但是,我在Rust中找不到代数类型下的任何文档。
什么是+
实际在这里做什么,它叫什么?我在哪里可以找到关于此的文档?
T: Any + Debug
是一个trait bound。类型T
必须满足Any
和Debug
,因此这里使用+
符号,它与代数类型无关。您可以在corresponding section in the book上阅读更多关于特征的信息。
This section提到+
标志。