Ownership-&-Lifecycle

In Value ownership and value lifecycle, value is usually referred to argument values in functions.

• read - immutable reference (this is default, if you don’t mention any)
• mut - mutable reference
• out - A special convention used for the self argument in constructor and named result. An out argument is uninitialized at the beginning of the function, and must be initialized before the function returns. Although out arguments show up in the argument list, they’re never passed in by the caller.
• var - function takes ownership of value, it can happen in two ways, he caller can transfer ownership (using ^) if not the callee might receive a newly-created value, or a copy of an existing value.
• deinit - Used in the destructor and consuming-move lifecycle methods

Here is the complete summary for var arguments in Mojo, covering every combination of struct capabilities and calling styles:

Logic	Struct Capability	WITHOUT ^	WITH ^
Pure Copy	__copyinit__ only	Copy (Original stays ✅)	Bitwise Move (Original dies ❌)
Pure Move	__moveinit__ only	Compile Error ❌	Move (Original dies ❌)
Standard	Both implemented	Copy (Original stays ✅)	Move (Original dies ❌)
Key Observations:

1. Without ^: Mojo tries to be safe. It will only let you pass the variable if it can safely duplicate it. If it can’t (no copy or move / or move-only type), it stops the program during compilation.
2. With ^: Mojo tries to be fast. It ignores your “Copy” logic entirely. Even if you haven’t written a “Move” constructor, it will perform a raw Bitwise Move of the fields to ensure the transfer happens with zero overhead.
3. The “Dead” State: Regardless of how the move happens (custom logic or bitwise), once you use ^, the original variable is gone. You cannot use it again in the same function.