Hands-On Design Patterns and Best Practices with Julia

The isa operator

The isa operator can be used to determine whether a value is a subtype of a type. For example, look at the following code:

Let me explain each of these results:

• The number 1 is an instance of the Int type, so it returns true.
• Because Float64 is a different concrete type, it returns false.
• Because Int is a subtype of Signed, which is a subtype of Integer, which is a subtype of Real, it returns true.

The isa operator could be useful for checking types in a function that accepts generic type arguments. For example, if the function can only work with Real numbers, then it may throw an error when a Complex value is passed by ...