Solidity – How to Define a Constant `bytes32` in Solidity v0.8 and Above

bytes32constantsoliditysolidity-0.8.x

I want to define a constant bytes32 like this:

bytes32 internal constant FOO = bytes32(0x01);

But I'm getting the following error when compiling the code above:

Explicit type conversion not allowed from "int_const 1" to "bytes32".

How can I do this in Solidity v0.8?

Best Answer

You just have to cast the constant values to uint256, like this:

bytes32 internal constant FOO = bytes32(uint256(0x01));

Note that you can also optionally ditch the hexadecimal prefix:

bytes32 internal constant FOO = bytes32(uint256(1));

Though you may want to keep it so that you remember that the value is a bytes32.

Related Solutions

Solidity Mapping – Can Mapping Be Called as Arguments of Function?

The second error you get tells you that external functions cannot have internal types as arguments (i.e. structs and mappings). You can solve that one by specifying internal or private for your function.

For the first error, im not sure if it is a bug or not, but you cannot pass mappings as arguments. What you could do is wrap them in a struct and pass the struct as a parameter.

One final notice is that if you declare your mapping as a state variable then you have access to it directly in your function. So in you example table could just be a state variable...especially since you only use it for storage purposes.

Solidity – Convert Bytes32 to Uint8 in Solidity 0.5.0

I don't think it ever was because bytes is a dynamic array of byte which means it has a length. Is it possible you saw bytes32 conversion to unit? That is totally acceptable in that both are 32-byte words.

This compiles under 0.4.25 as well 0.5.2.

contract Bytes {

    function convert(bytes32 b) public pure returns(uint) {
        return uint(b);
    }
}

On the other hand, this conversion is trouble in all cases I'm aware of.

contract Bytes {

    function convert(bytes b) public pure returns(uint) {
        return uint(b);
    }
}

In my opinion, conversion of bytes and string to numbers, string manipulation, etc. are problematic issues that should usually be dealt with by software clients rather than burdening contracts with such concerns. It's a case where the contract team should strongly resist overloading the contract with concerns that software clients are capable of resolving.

Hope it helps.

Best Answer

Related Solutions

Solidity Mapping – Can Mapping Be Called as Arguments of Function?

Solidity – Convert Bytes32 to Uint8 in Solidity 0.5.0

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