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I have a contract called Erc20Recover in which I have the following function:

pragma solidity >=0.8.0; contract Erc20Recover { function _setNonRecoverableTokens(IErc20[] calldata tokens) public { // ... } }

I have another contract called HToken which inherits from Erc20Recover and in whose constructor I attempted to call _setNonRecoverableTokens:

pragma solidity >=0.8.0; contract HToken is Erc20Recover { constructor(underlying) { IErc20[1] memory nonRecoverableTokens = [underlying]; _setNonRecoverableTokens(nonRecoverableTokens); } }

But the code does not compile:

Invalid type for argument in function call. Invalid implicit conversion from contract IErc20[1] memory to contract IErc20[] calldata requested.

How can I turn that in-memory static array into a calldata array? Or, more generally, how can I call _setNonRecoverableTokens?

For context: IErc20 is my implementation of the ERC-20 interface.

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  • I couldn't figure out how to make the conversion from memory to calldata but I fixed my problem by defining the tokens array as memory. Commented Sep 14, 2021 at 16:42

2 Answers 2

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It's not possible to copy data from memory to calldata. Calldata, being the cheapest type of storage, is read-only and can only be used for data passed in to a function through the transaction input.

From the Solidity documentation:

As already said, the called contract (which can be the same as the caller) will receive a freshly cleared instance of memory and has access to the call payload - which will be provided in a separate area called the calldata.

As you mentioned in the comments, simply using memory instead of calldata for tokens solves the issue. If you're calling the contract through a transaction, this will simply copy the calldata to the memory.

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  • Does it cost more gas the way I defined with memory? Commented Sep 14, 2021 at 18:19
  • It costs slightly gas more to use memory instead of calldata, since the input data needs to be copied to memory. Commented Sep 15, 2021 at 11:03
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Besides what Morten wrote, one can do this._setNonRecoverableTokens(nonRecoverableTokens); to call _setNonRecoverableTokens externally which will copy your memory array to calldata (see slide '57' here). However, calling function externally will also lead to creation of a new context besides incurring previous copy operation, so, calling function internally (which happens by simple jumps) is generally more efficient.

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