原文链接 https://liutaihua.github.io/2015/12/20/rust-func-as-function-arg-type.html
注：以下为加速网络访问所做的原文缓存，经过重新格式化，可能存在格式方面的问题，或偶有遗漏信息，请以原文为准。
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Rust: func as function arg
在很久很久以前， 其实特么也不是很久， rust以前能直接用closure作为参数类型传参，结果现在在rustc 1.5下试了一下， 根本不行啊:
fn call_fun(f: |i32| -> i32) { // error: expected type, found |
println!("call func got res: {}", f(32));
}
fn call_function(function: fn(u8) -> bool) -> bool { // fix error of the above
function(8)
}
fn main() {
let max = 5;
let closure = move |arg: u8| { arg < max };
println!("{}", call_function(closure));
}
// 编译会产生下面的错误
// test.rs:18:34: 18:41 error: mismatched types:
// expected fn(u8) -> bool,
// found [closure@tt.rs:17:19: 17:47 max:_]
// (expected fn pointer,
// found closure) [E0308]
// tt.rs:18 println!("{}", call_function(closure));
// ^~~~~~~
只能说以前看到的rust语法已经在后续的发展中修改了。 那么我们现在变成这样的做法了：fn call_function(function: fn(u8) -> bool) -> bool {
function(8)
}
fn my_local_function(arg: u8) -> bool{
let max = 5;
arg < max
}
fn main() {
println!("{}", call_function(my_local_function));
}
它的泛型用法：fn call_function(function: fn(u8) -> bool) -> bool {
function(8)
}
fn my_local_function(arg: u8) -> bool{
let max = 5;
arg < max
}
fn main() {
println!("{}", call_function(my_local_function));
fn double(x: i32) -> i32 {x + x}; // Ok
println!("Res is {}", call_twice(10i32, double)); // OK
let closure = |x: i32| -> i32 {x + x};
println!("Closure res is {}", call_twice(10i32, closure));
}
fn call_twice<A, F>(val: A, f: F) -> A where F: Fn(A)->A {
let tmp = f(val);
f(tmp)
}
总的说， 就是函数声明语义， 已经不能中参数类型中， 直接用匿名函数来表示参数的类型了； 这里还有一个方式， 就是用Trait的方式， 也可以做到func as arg type：trait FunctionCaller {
fn call_function(&self, function: &Fn(u8) -> bool) -> bool;
}
struct MyFunctionCaller {
data: u8,
}
impl FunctionCaller for MyFunctionCaller {
fn call_function(&self, function: &Fn(u8) -> bool) -> bool {
function(self.data)
}
}
fn main() {
let my_function_caller = &MyFunctionCaller{data: 8};
println!("{}", invoke(my_function_caller));
}
fn invoke(function_caller: &FunctionCaller) -> bool {
let max = 5;
let closure = &move |arg: u8| { arg < max };
function_caller.call_function(closure)
}