2.14 Keywords & Shorthand Operators

Shorthand Operators

These are concise notations of slightly longer expressions as shown here

Long expression	Shorthand notation
a = a + e	a += e
a = a - e	a -= e
a = a*e	a *= e
a = a/e	a /= e
a = a%e	a %= e
a = a|e	a |= e
a = a&e	a &= e
a = a^e	a ^= e

Basically it consists on simplifying the expression of increments and decrements, where the result of the expression the value of a after the increment or decrement has been performed.

Delete

The delete keyword that can be used within smart contracts to reclaim the underlying storage of a variable when it is no longer required in in that context of the contract. Applying this keyword on a variable a, of a particular type, assigns the initial value for that type to a.

So if it is applied on integers, then the value of that variable is set to 0, for arrays it assigns a length of 0. For dynamic arrays and for static arrays the length remains the same but all the elements are set to their initial value.

delete A[x] where A is an array and x specifies a particular index, deletes the item at that index of that array and leaves all the other elements and even the length of that array intact.

For structs, delete assigns a struct with all the members reset to their initial values. Delete has no effect on mappings, this is an exception that has to be paid attention to. So if you delete a struct which in turn has a mapping as one of its fields, then delete will reset all the members of that struct that are not mappings and will also recurse into each of those members unless they are mappings. But if you want to delete a particular key of that mapping then that is possible.

Reserved Keywords

These are keywords in Solidity that are reserved for future use, so they are not currently used by any of the syntax that is supported. These may be used for any anticipated new syntactic features within Solidity.

There are many such reserved keywords, some of them are: after, alias, apply, auto, case, null, etc...

You can imagine why these could potentially be reserved: because they all have a specific significance in the context of programming languages (especially object-oriented programming languages). Solidity anticipates that it may support features that may end up using these reserved keywords.

An example of a keyword that was reserved earlier is unchecked, which is now used as of version 0.8.0 for declaring any block within Solidity as being unchecked for arithmetic overflow and underflow checks. So we can assume that some of these reserved keywords might be supported in future Solidity versions for different features.