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There is no way in solidity to check if an address is a contract. One of the goals of Ethereum is for humans and smart contracts to both be treated equally.2 o) M" m" Z8 E
https://stackoverflow.com/a/37670490/7218912; m, u: @, i7 j( S
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有时候确实有需要向智能合约转账:
但是大多数 smart contract 的 token 是不能转出的,只要合约里没写转出的逻辑,就不能转出。以太坊将智能合约看做是独立的个体,没人知道它的私钥,给不支持转出的智能合约转 token 就等于销毁了。. d+ w* M2 j( _# ^* E8 ^3 _7 F6 G* g
当我们要转账时,会转到交易方的地址,不会闲着没事给智能合约转 token。但是这种事情仍然会发生,不断有人给 EOSTokenContract 转 EOS(见下图),EOSTokenContract 账户下现在有 154,834 EOS,价值 $1,176,738.4(价格 $7.6)。类似的,QtumTokenContract 账户下现在有 22,293 QTUM,价值 $158,280.3(价格 $7.1)。* A: \- H- A4 Q% h: z0 X
这些 token 都都都都销毁了 (⊙?⊙)
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Dexaran 认识到了这个问题," A0 V5 N0 `( r k+ z
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Contracts that are not designed to work with tokens must reject incoming token transactions. Otherwise, each token becomes a potential token trap.: J' J6 d9 c. |; `9 H I- @
ERC20 token standard issues.(google docs)
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并在 github 创建了一个 issue。
tokenFallback 函数,当转账到不能转出的智能合约地址时,将自动取消。
contract ERC223 {
function transfer(address to, uint value, bytes data) {: F8 J6 w& w8 f6 u& f9 t1 Y* ~
uint codeLength;9 g, r% k, o7 {: X
assembly {
codeLength := extcodesize(_to)2 ?7 |* E, S: {5 S1 f: ~8 s
} q/ q: C3 N% b+ o& b, \4 z; U
balances[msg.sender] = balances[msg.sender].sub(_value);
balances[_to] = balances[_to].add(_value);
if(codeLength>0) {! p+ Z! z1 o0 g2 k' Y) U
// Require proper transaction handling.6 O) s G* T" ~' z8 _) c
ERC223Receiver receiver = ERC223Receiver(_to);! i G2 _) W' s2 q+ M% i: \
receiver.tokenFallback(msg.sender, _value, _data);
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}
}
【todo】:代码解释7 i/ [- |% @0 b' L, k
The biggest change is that ERC223 no longer allow token to be transferred to a contract that does not allow token to be withdrawn.
https://medium.com/cryptomover/what-are-erc20-and-erc223-tokens-307badcca5a