Kevin Wang

Related: https://github.com/briansmith/ring/pull/1499

 This is the use case.

Would the `pallet-contracts` running ink! 4.0 contracts can also run ink! 3.0 contracts?

See also: https://github.com/rust-lang/rust/issues/57640

> 对于 `实类型` 来说， `trait bound` 是一种具有 `排除性质` 的限定， `trait bound` 不关注 `实类型` 到底实现多少方法，只关注 `实类型` 没有实现的方法，一旦 `实类型` 没有实现 `trait bound` 中的全部方法，就标记该 `实类型` 不符合 `trait bound` 检查bound的时候，只需要检查有没有impl这个trait就好了，不用逐个检查方法有没有实现。impl的时候才会检查有没有实现全。

> @kvinwang can you give us a couple more details as to why a non-freeing allocator is a problem for your off-chain env? In our case, we run the contract...

@nlordell Your suggestions applied. Thanks.

Another [issue](https://github.com/paritytech/ink/issues/1535) with the bump allocator. Should we consider this feature request?

> Can I ask you to compare the contract sizes of contracts which use a) our bump allocator b) `wee_alloc` and c) `dlmalloc-rs`? Sorry for the latency to reply due...

Rebased onto master