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GitBook: [snapshot-labs#7] WIP: how to write a basic strategy
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| description: Main components of a basic strategy | ||
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| # How to write a basic strategy | ||
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| Every strategy is, at its core, the implementation of the `strategy(space, network, provider, addresses, options, snapshot)` function. | ||
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| A quick word on the function parameters: | ||
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| * `space`: the space (if applicable), based on the registered ENS associated with this strategy (see [Spaces](../spaces/)) | ||
| * `network`: the network id as an integer (1 for Ethereum) | ||
| * `provider`: the network provider used by the web browser | ||
| * `addresses`: the list of addresses of the voters being processed. | ||
| * `options`: a collection of options that can be passed to strategy(...) - those have no default keys and can be used to pass any useful data | ||
| * `snapshots`: the block height at which the data are queried by strategy(...) - if none is passed, 'latest' is used.  | ||
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| `Strategy(...)` returns a javascript object with every addresses from the addresses array as keys and the corresponding voting power as value (expressed in number of token owned by the address for `erc20-balance-of`, as a number of rocks owned for `has-rock`, etc). | ||
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| Every strategy comes with a JSON file `examples.json`. This file is mandatory as it will be used for testing and validating the strategy before including it in Snapshot main GitHub branch. Here are the main keys: | ||
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| * `"name"`: a human-reading name for the strategy ("ERC20 balance" for instance). | ||
| * `"strategy"`: the core parameters of the strategy | ||
| * `"name"`: the strategy name ("erc20-balance-of") | ||
| * `"params"`: optional parameters passed in `options` to strategy(...). Any useful "key":"value" can be used here and retrieved inside `strategy(...)` via `options.key` | ||
| * `"address"`: the address of the token contract (the DAI contract for instance) | ||
| * `"symbol"`: the token symbol ("DAI") | ||
| * `"decimals"`: the number of decimals (18) | ||
| * `"network"`: the network id (1 for ethereum) | ||
| * `"addresses"`: an array of addresses which will be used for testing (they should therefore have some token) | ||
| * `"snapshot"`: the block height (by taking a block height in the past where the addresses\[] had a positive balance, the test will be easily repeated) | ||
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| Finally, all strategies will contain some similar steps, illustrated in [erc20-balance-of](https://github.com/snapshot-labs/snapshot-strategies/blob/f41f98249cff78486914473a3fef29ea960971e5/src/strategies/erc20-balance-of/index.ts): | ||
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| * Getting the block height ('latest' or a specific one via the `snapshot` argument). | ||
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| ``` | ||
| const blockTag = typeof snapshot === 'number' ? snapshot : 'latest'; | ||
| ``` | ||
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| * Initializing Multicaller: looping over the addresses\[] array is **not allowed** as the strategy complexity would increase with the array size. Instead, Snapshot provides the Multicaller utility to group blockchain queries for a series of addresses. The abi can be in ethers human-readable form ( `['function balanceOf(address account) external view returns (uint256)']` for instance) | ||
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| ``` | ||
| const multi = new Multicaller(network, provider, abi, { blockTag }); | ||
| ``` | ||
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| * Feeding data into the multicaller and executing the multicall: every query is queued in the multicaller via `Multicaller.call(...)`. Once they are all stored, an unique call is executed via `Multicall.execute()`.  | ||
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| `option.address` is the token contract address (`strategy.params.address` in `examples.json`). | ||
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| ``` | ||
| addresses.forEach((address) => | ||
| multi.call(address, options.address, 'balanceOf', [address]) | ||
| ); | ||
| const result: Record<string, BigNumberish> = await multi.execute(); | ||
| ``` | ||
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| * Creating an object where every address from addresses\[] is paired with its corresponding value (returned from the multicall) and returning it | ||
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| ``` | ||
| return Object.fromEntries( | ||
| Object.entries(result).map(([address, balance]) => [ | ||
| address, | ||
| parseFloat(formatUnits(balance, options.decimals)) | ||
| ]) | ||
| ); | ||
| ``` |