3.20 Unary Expressions

Unary Expressions

Unary expressions are where an operator is used on a single operand as opposed to two operands, in which case it would be a binary expression. Such unary expressions are susceptible to typographical errors by developers.

For example let's take a look at the scenario where there's a variable x. The developer wants to increment it by one, so the way to do that is to say x += 1 which effectively is x = x + 1. But if the developer interchanges the order of + and = and instead uses x = +1, then this would result in re-initializing the value of x to +1. The reason for this is that + 1 is a unary expression whose value is 1 and x would get initialized to that value.

As you can imagine such typographical errors are likely to be made by developers it's very easy to make these switching the order and, if they are considered as valid by the compiler, then it's very hard to notice such errors both by the developer as well as by the security auditor.

So in order to prevent some of the most common usages that result in such typographical errors the unary + was deprecated as of compiler Solidity version 0.5.0.

Long Number Literals

There is a security risk in the use of long number literals within Solidity contracts. These number literals may require many digits to represent their high values (as constants) or many decimal digits of precision, which as you can imagine is error prone.

For example, if one were to define a variable representing Ether, then it would need to be assigned a number literal that has 18 zeros to represent the 18 decimals of precision.

So the developer may accidentally use an extra zero or miss a zero in which case the Ether precision is different, thus the logic using this variable will be broken.

The best practice here is to use the Ether or time suffixes supported by Solidity as applicable or to use the Scientific Notation which is also supported by Solidity.