We saw in this chapter that code in Julia is represented by expressions that are data structures of the Expr type. The structure of a program and its types can therefore be explored programmatically just like any other data. This means that a running program can dynamically discover its own properties, which is called reflection. We have already encountered some of these macros or functions before:
- Use the @isdefined macro to check whether a variable is already declared, for example if a is not declared, you get:
@isdefined a #> false
- Use the typeof and InteractiveUtils.subtypes to query the type hierarchy (refer to Chapter 6, More on Types, Methods, and Modules)
- Use the methods(f) to see all the methods of a function f (refer to Chapter 3, Functions)
- names and types: given a type Person:
mutable struct Person
name:: String
height...