Casting

[reyalabs]

• Ensure casting between types is done deliberately everywhere in the codebase, based on a suggestion from CR: "We should also standardise conversion/casting between any two number representations, and ensure bounds are checked when casting (can't remember whether solidity now does this)."

[CyclopsRex]

As with user defined types, I don't think we should be making wholesale changes to standardise things at this late stage, but it's always worth paying close attention to casting and looking for potential issues with underflow/overflow/rounding.