It is a common pattern to validate required preconditions at the beginning of a function or block. There are two different kinds of
preconditions:
- Preconditions about argument values. An example is the assertion that a function argument lies within a specific range. An
IllegalArgumentException should be thrown if these preconditions are violated.
- Preconditions about the state of the owner or the execution context of the function. An example is when a specific method, such as
open, init or prepare, must be called before the current method can be executed. An
IllegalStateException should be thrown if these preconditions are violated.
The Kotlin standard library provides the functions check(), require(), checkNotNull() and
requireNotNull() for this purpose. They should be used instead of directly throwing an IllegalArgumentException or an
IllegalStateException.
What is the potential impact?
Readability and Understanding
This change makes it easier to understand the code because the semantics of check(), require(),
checkNotNull() and requireNotNull(), as well as the fact that this is a preconditions check, are evident to the reader. When
developers share common standards and idioms, they need to spend less effort understanding each other’s code.
Code Redundancy
Using a built-in language feature or a standard API is always better than a custom implementation, because the reimplementation of something that
already exists is unnecessary.
Consistency
When check(), require(), checkNotNull() and requireNotNull() are used in an idiomatic way,
there is more consistency in what kind of exception is thrown in which situation.
