Add "equals" method to SafeMath

[rbval]

🎉 Description

Add "equals" to SafeMath. Currently mul / div / sub / add create a clean syntax. It would be nice to have an "equals" operation that could be added to require statements and return values.

• 📈 This is a feature request.

📝 Details

In detail this could be used for example like this inside methods:

require(x.equals(0));
return x.equals(0);

[nventuro]

Hi @rbval! What would the purpose of such a function be? AFAIK, there's no scenario in which == may throw or not return the correct value.

[barakman]

@rbval:

Maybe you got the inspiration for this from off-chain code that you have at hand (e.g., Javascript assert module, which is often used in Truffle tests), where equals may be used for comparison between variables of different types.

In the on-chain side, such function would be absolutely worthless.
If you want to compare between variables of different types, then you need to explicitly cast one (or both) of them. A generic cast (such as template in C++) is not supported in the Solidity language.

In addition to that, all the functions in SafeMath are wrappers for the Solidity language arithmetic operators, allowing the user to execute them "safely".
A wrapper for the Boolean operator == will not provide any additional functionality here, nor will it make the code look "cleaner" (if that's what you had in mind).

[rbval]

I think you are both right. One more poke: in the sub method there’s a requirement the first number to be greater than the second one. I believe this is due to not getting output of a negative number. Could that be applied here where we could demand both numbers to be greater than zero ( > 0 ) before comparing them as two integer overflowed numbers can be equal and possible currently? I think the compiler throws warnings but it could be a good safe method? @nventuro @barakman

[nventuro]

If you use SafeMath.add, you will never get an overflow (that will cause execution to halt). Other than that, it is not possible to detect if an uint256 has been overflowed or not, since all values in the domain are equally valid. The one that I'm not sure about is casting a signed integer to unsigned, Solidity may do runtime checks on those.

Closing the issue.