不匹配的類型：`預期FN @（@ &&型） - > uint`但發現`的extern FN（@map_a） - > uint`（預期參數模式++但發現&&）

Question

$ rustc --test mapAsMapKey.rs 
mapAsMapKey.rs:18:43: 18:52 error: mismatched types: expected `fn@(&&@map_a) -> uint` but found `extern fn(@map_a) -> uint` (expected argument mode ++ but found &&) 
mapAsMapKey.rs:18  let b: map_b = hashmap::<@map_a, uint>(rmap_hash, rmap_eqer); 
                  ^~~~~~~~~ 
mapAsMapKey.rs:18:54: 18:63 error: mismatched types: expected `fn@(&&@map_a, &&@map_a) -> bool` but found `extern fn(@map_a, @map_b) -> bool` (expected argument mode ++ but found &&) 
mapAsMapKey.rs:18  let b: map_b = hashmap::<@map_a, uint>(rmap_hash, rmap_eqer); 
                     ^~~~~~~~~ 
error: aborting due to 2 previous errors 

防鏽功能：

fn rmap_hash (m: @map_a) -> uint { 0 } 
fn rmap_eqer (m1: @map_a, m2: @map_b) -> bool { true } 

行觸發：

let b: map_b = hashmap::<@map_a, uint>(rmap_hash, rmap_eqer); 

Answer 1

請問，如果你寫這樣的防鏽功能，它的工作？

fn rmap_hash (&&m: @map_a) -> uint { 0 } 

fn rmap_eqer (&&m1: @map_a, &&m2: @map_b) -> bool { true }