Structures

Structures are copied when used as an initial value for constant or variable, when assigned to a different variable, when passed as an argument to a function, and when returned from a function.

Accessing a field or calling a function of a structure does not copy it.

// Declare a structure named `SomeStruct`, with a variable integer field.
//
pub struct SomeStruct {
    pub var value: Int

    init(value: Int) {
        self.value = value
    }

    fun increment() {
        self.value = self.value + 1
    }
}

// Declare a constant with value of structure type `SomeStruct`.
//
let a = SomeStruct(value: 0)

// *Copy* the structure value into a new constant.
//
let b = a

b.value = 1
// NOTE: `b.value` is 1, `a.value` is *`0`*

b.increment()
// `b.value` is 2, `a.value` is `0`