有个编译错误，把pub改成pub(crate)后就解决了，但是不知道为什么。

Question

写了个闭包作为参数的函数：

pub fn internal_creator_use_twitter_pool<F>(&mut self, pool_id: &PoolId, mut f: F) 
    where F: FnMut(&mut TwitterPool);

结果编译就报：

error[E0277]: the trait bound `F: near_sdk::serde::Serialize` is not satisfied
   --> src/twitter_giveaway.rs:148:1
    |
148 | #[near_bindgen]
    | ^^^^^^^^^^^^^^^ the trait `near_sdk::serde::Serialize` is not implemented for `F`
    | 
   ::: /Users/xxx/.cargo/registry/src/github.com-1ecc6299db9ec823/serde_json-1.0.68/src/value/mod.rs:940:8
    |
940 |     T: Serialize,
    |        --------- required by this bound in `to_value`
    |
    = note: required because of the requirements on the impl of `near_sdk::serde::Serialize` for `&F`
    = note: this error originates in the macro `json_internal` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider restricting type parameter `F`
    |
160 |     pub fn internal_creator_use_twitter_pool<F: near_sdk::serde::Serialize>(&mut self, pool_id: &PoolId,mut f: F)
    |                                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

改成pub(crate)后，编译通过，但是不懂为什么。

Answer 1

可见度不同

• pub(crate) 在当前crate中可见, 外部 crate 不可见
• pub 在外部 crate 可见

pub 比 pub(crate) 可见度高, 可能有冲突