Updated up to Changelog v0.6.1 (2023-12-18)
owned and inout are different:
If the value passed is not owned, it is not possible to delete it🗑️,
MyType.__del__(owned self) require the argument passed as owned.
If a value is passed as inout, it is possible to assign it a new value ✍:
MyType.__init__(inout self).
This is great because the function can modify it, so it is named a mutable reference.
Additionally, the function could not free it, wich makes it safer🛡️.
Like 🗑️del, owned arguments are require to 🏗️move values:
__del__(owned self)__moveinit__(inout self,owned other:Self)
Once the value got passed^ as owned to a function, we can't use it anymore !
Unless the function returns it back or store it somewhere.
struct MyType:
var value:Int
fn __init__(inout self, v:Int): self.value = v
fn __moveinit__(inout self, owned other: Self): #🏗️
self.value = other.value
var BackupValue:MyType = 0
fn MoveIn(owned v:MyType):
print(v.value)
v.value = 123456
BackupValue = v^
fn main():
BackupValue = 0
var a:MyType = 123
MoveIn(a^)
#print(a.value) # use of uninitialized value 'a'
print(BackupValue.value) #✅ 123456(Note that global variables need to be initialized)
⚠️ If the type also implementcopyinit, owned instances of a copy could be passed!
@value #⚠️ Synthesise also __copyinit__
struct StackOfBricks:
var amount:Int
fn __moveinit__(inout self,owned other:Self):
self.amount = other.amountstruct Home(Movable):
var bricks:Int #🧱
#🏚️👷🧱
fn __init__(inout self, initialamount:Int=0):
self.bricks = initialamount
#🏠🏗️🏚️ Move bricks in
fn __moveinit__(inout self,owned other:Self): #A_self=B_other^
self.bricks = other.bricks
#🏚️🏗️🏠 Move bricks out
fn MoveTo(owned self,inout other:Self):
other = self^ #Home.__moveinit__(other,self^)
#🏠🏗️📈🏗️❔
fn AddOneBrick(owned self)->Self:
self.bricks+=1 #ex: var A = Home.increment(A^)
#ex: var B = A^.increment()
return self^
#🏠🏗️📈🏗️❔
fn AddOneBrickFromStackOfBricks(owned self,inout s:StackOfBricks)->Self:
if s.amount > 0:
s.amount-=1 #ex: var x:Int = 10
self.bricks+=1 #ex: var A = Home.increment(A^,x)
return self^
fn AddAllBricksFromStackOfBricks(inout self,owned other:StackOfBricks):
self.bricks += other.amount
# other is not used after, automatically __del__() here.
#_ = other^ # manually
#similar to: StackOfBricks.__del__(other^) manually
fn AddBricksFrom(inout self,inout other:Self,amount: Int):
if amount<= other.bricks:
self.bricks+=amount
other.bricks -= amount
#🏠🏗️🗑️
fn __del__(owned self): #Home.__del__(A^)
#ex: self.somepointer.free()
... #🏠🏗️📈🏗️❔
fn AddBrick(owned arg:Home)->Home:
arg.bricks+=1
return arg^ #➡️🏗️
fn main():
var location_a = Home(initialamount=10) #🟦
var location_b = Home(initialamount=0) #🟨
print(location_a.bricks) #🟦1️⃣0️⃣
print(location_b.bricks) #🟨0️⃣
location_b = location_a^ #🟦➡️🏗️🟨
print(location_b.bricks) #🟨1️⃣0️⃣
#print(location_a.bricks) #🟦❌✋ use of uninitialized value 'location_a'
#🟨🏠 #1️⃣0️⃣
#🟦🏚️ #__del__() been called on it
location_b = AddBrick(location_b^) #🟨🏗️📈🏗️🟨
print(location_b.bricks) #🟨1️⃣1️⃣
location_a = Home(0) #🟦0️⃣
var BrickStack = StackOfBricks(4) #🧱4️⃣
#Bricks stack argument is inout:
location_a = location_a^.AddOneBrickFromStackOfBricks(BrickStack)
print(location_a.bricks) #🟦1️⃣
print(BrickStack.amount) #🧱3️⃣
#Bricks stack argument is owned:
location_a.AddAllBricksFromStackOfBricks(BrickStack^)
print(location_a.bricks) #🟦4️⃣
#print(BrickStack.amount) #🧱❌✋ use of uninitialized value 'BrickStack'
location_a^.MoveTo(location_b) #🟦➡️🏗️🟨
print(location_b.bricks) #🟨4️⃣
#print(location_a.bricks) #🟦❌✋
location_a = Home(0) #🟦0️⃣
location_b = Home(10) #🟨1️⃣0️⃣
#location a and b are inout argument:
location_a.AddBricksFrom(location_b,5)
location_a.AddBricksFrom(location_b,1)
#inout arguments are not moved, only owned ones
print(location_a.bricks) #🟦6️⃣
print(location_b.bricks) #🟨4️⃣
location_b.AddBricksFrom(location_a,6)
print(location_a.bricks) #🟦0️⃣
print(location_b.bricks) #🟨1️⃣0️⃣
var BrickStackOne = StackOfBricks(30)#🧱🔵3️⃣0️⃣
var BrickStackTwo = StackOfBricks(20)#🧱🟡2️⃣0️⃣
var BigStackOfBrick = JoinBrickStacks(BrickStackOne^,BrickStackTwo^)
print(BigStackOfBrick.amount) #🧱🟢5️⃣0️⃣
#print(BrickStackOne.amount) #🧱🔵❌✋
#print(BrickStackTwo.amount) #🧱🟡❌✋
_ = BigStackOfBrick # ⚠️ will not delete it
# @value generate __copyinit()__
# so it will delete a copy
# Successful with the ^ suffix
BigStackOfBrick^.__del__()
#similar to:
# _ = BigStackOfBrick^
# StackOfBricks.__del__(BigStackOfBrick^)
#print(BigStackOfBrick.amount) #🧱🟢❌✋
#The ^suffix allow to treat the value as owned!
# 🏗️ Movable trait (see 🔸function below):
var Val_C = StackOfBricks(10)
var Val_D = StackOfBricks(0)
MoveTo(Val_C^,Val_D)
#StackOfBricks also implement __moveinit__() (@value also make it!)
Val_C = StackOfBricks(10)
#T is passed explicitely, but mojo can deduce it(see above)
MoveTo[StackOfBricks](Val_C^,Val_D)
#🔸
fn MoveTo[T:Movable](owned a:T,inout b:T):
#The Movable trait means the type passed implement __moveinit__()
#similar to: T.__moveinit__(b,a^)
b=a^
fn JoinBrickStacks(owned a:StackOfBricks, owned b:StackOfBricks) -> StackOfBricks:
var total = a.amount + b.amount
return StackOfBricks(total)
⚠️ Could contains errors, make sure to see mojo repo or documentation website for better materials