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67 lines
3.3 KiB
Markdown
67 lines
3.3 KiB
Markdown
## ERC20
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<br>
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* defines a common interface for contracts implementing this token, such that any compatible token can be accessed and used in the same way.
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* a transaction sending ether to an address changes the state of an address. a transaction transferring a token to an address only changes the state of the token contract, not the state of the recipient address.
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* one of the main reasons for the success of EIP-20 tokens is in the interplay between `approve` and `transferFrom`, which allows for tokens to not
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only be transferred between externally owned accounts (EOA).
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- but to be used in other contracts under application specific conditions by abstracting away `msg.sender` as the mechanism for token access control.
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* a limiting factor lies from the fact that the EIP-20 `approve` function is defined in terms of `msg.sender`.
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- this means that user’s initial action involving EIP-20 tokens must be performed by an EOA.
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- if the user needs to interact with a smart contract, then they need to make 2 transactions (`approve` and the smart contract internal call `transferFrom`), with gas costs.
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<br>
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---
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### ERC20-compliant token contract
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<br>
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* `totalSupply`: Returns the total units of this token that currently exist. ERC20 tokens can have a fixed or a variable supply.
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* `balanceOf`: Given an address, returns the token balance of that address.
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* `transfer`: Given an address and amount, transfers that amount of tokens to that address, from the balance of the address that executed the transfer.
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* `transferFrom`: Given a sender, recipient, and amount, transfers tokens from one account to another. Used in combination with approve.
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* `approve`: given a recipient address and amount, authorizes that address to execute several transfers up to that amount, from the account that issued the approval.
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* `allowance`: given an owner address and a spender address, returns the remaining amount that the spender is approved to withdraw from the owner.
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* `Transfer`: event triggered upon a successful transfer (call to transfer or transferFrom) (even for zero-value transfers).
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* `Approval`: event logged upon a successful call to approve.
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<br>
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---
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### ERC20 optional functions
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<br>
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* in addition to the required functions listed in the previous section, the following optional functions are also defined by the standard:
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- `name`: returns the human-readable name (e.g., "US Dollars") of the token.
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- `symbol`: returns a human-readable symbol (e.g., "USD") for the token.
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- `decimals`: returns the number of decimals used to divide token amounts. For example, if decimals is 2, then the token amount is divided by 100 to get its user representation.
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<br>
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---
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### the ERC20 interface
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<br>
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```
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contract ERC20 {
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function totalSupply() constant returns (uint theTotalSupply);
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function balanceOf(address _owner) constant returns (uint balance);
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function transfer(address _to, uint _value) returns (bool success);
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function transferFrom(address _from, address _to, uint _value) returns
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(bool success);
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function approve(address _spender, uint _value) returns (bool success);
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function allowance(address _owner, address _spender) constant returns
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(uint remaining);
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event Transfer(address indexed _from, address indexed _to, uint _value);
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event Approval(address indexed _owner, address indexed _spender, uint _value);
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}
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```
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