As you read Rust code you will see many function calls that have an exclamation mark ! at the end.
Some of the most common ones are:
In reality, these are called macros. They are replaced by more Rust code at compile time.
There are a number of macros in the standard library and there are many crates sharing additional macros.
Macros can be useful to eliminate duplicate code that for some reason we cannot, or do not want to put in a function.
They can also include Rust code that would be executed during the compilation of the code.
