@value
You can add the @value
decorator on a struct to generate boilerplate
lifecycle methods, including the member-wise __init__()
constructor,
__copyinit__()
copy constructor, and __moveinit__()
move constructor.
For example, consider a simple struct like this:
@value
struct MyPet:
var name: String
var age: Int
@value
struct MyPet:
var name: String
var age: Int
Mojo sees the @value
decorator and notices that you don't have any constructors
and it synthesizes them for you, the result being as if you had actually
written this:
struct MyPet:
var name: String
var age: Int
fn __init__(inout self, owned name: String, age: Int):
self.name = name^
self.age = age
fn __copyinit__(inout self, existing: Self):
self.name = existing.name
self.age = existing.age
fn __moveinit__(inout self, owned existing: Self):
self.name = existing.name^
self.age = existing.age
struct MyPet:
var name: String
var age: Int
fn __init__(inout self, owned name: String, age: Int):
self.name = name^
self.age = age
fn __copyinit__(inout self, existing: Self):
self.name = existing.name
self.age = existing.age
fn __moveinit__(inout self, owned existing: Self):
self.name = existing.name^
self.age = existing.age
Mojo synthesizes each lifecycle method only when it doesn't exist, so
you can use @value
and still define your own versions to override the default
behavior. For example, it is fairly common to use the default member-wise and
move constructor, but create a custom copy constructor.
For more information about these lifecycle methods, read Life of a value.
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