Working with Structs
Objects created from classes take up heap memory, and the garbage collector needs to release that. As you saw in the loop code in Structuring a Class, creating many objects can quickly consume a lot of resources. To boost performance in such a case, you can use a sort of lightweight class called struct, which inherits from class Struct.
Structs are allocated in stack memory, so a struct is copied when reassigned or passed to a method. In other words: it’s passed by value. At first sight, they look very much like classes: they have properties, constructors, and methods, and they can even be generic.
The following example defines a struct to accommodate user data:
| | struct User |
| | property name, age |
| | |
| | def initialize(@name : String, @age : Int32) |
| | end |
| | |
| | def print |
| | puts "#{age} - #{name}" |
| | end |
| | end |
| | |
| | d = User.new("Donald", 42) |
| | d.name # => Donald |
| | d.age = 78 |
| | d.print # => 78 - Donald |
Changing Structs in Methods | |||||||||||||||||||||||||||||||
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Because structs are copied when passed, you must think about returning the value and reassigning it after return. In the following snippet, the no_change method doesn’t change the struct, only the change method works:
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Structs work best for non-changing (also called immutable) data structures, especially when the structure is small and you have lots of them. As a good example, the standard library implements complex numbers through the struct Complex.
Inheritance can also be defined for a struct, but only from an abstract struct.
Use Structs for Performance | |
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Try changing class to struct in your code and see if it enhances performance. If it does and it fits with the functionality, go for it. |
Your Turn 3
➤ Vec2D—Overloading an Operator on a Struct: Suppose you need to add lots of two-dimensional vectors. Define a struct Vec2D for doing just that and overload the + operator. Then define a few of them and work with these vectors. (Hint: Restrict the + operation to adding another Vec2D by using self.)