Design Decisions

The following sections describe some of the notable design decisions made in the Soroswap Protocol. These are safe to skip unless you're interested in gaining a deep technical understanding of how the protocol works under the hood, or writing smart contract integrations!

Sending Tokens

Typically, smart contracts which need tokens to perform some functionality require would-be interactors to first make an approval on the token contract, then call a function that in turn calls transferFrom on the token contract. This is not how V2 pairs accept tokens. Instead, pairs check their token balances at the end of every interaction. Then, at the beginning of the next interaction, current balances are differenced against the stored values to determine the amount of tokens that were sent by the current interactor. See the whitepaper for a justification of why this is the case, but the takeaway is that tokens must be transferred to the pair before calling any token-requiring method (the one exception to this rule is Flash Swaps).


Unlike Uniswap V1 pools, V2 pairs do not support ETH directly, so ETH⇄ERC-20 pairs must be emulated with WETH. The motivation behind this choice was to remove ETH-specific code in the core, resulting in a leaner codebase. End users can be kept fully ignorant of this implementation detail, however, by simply wrapping/unwrapping ETH in the periphery.

The router fully supports interacting with any WETH pair via ETH.

Minimum Liquidity

To ameliorate rounding errors and increase the theoretical minimum tick size for liquidity provision, pairs burn the first MINIMUM_LIQUIDITY pool tokens. For the vast majority of pairs, this will represent a trivial value. The burning happens automatically during the first liquidity provision, after which point the totalSupply is forevermore bounded.

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