Version: 1.1.0

Value semantics

Mojo defaults to value semantics. A function receives its own view of the data unless you deliberately pass a reference.

Essentials

• Copying a List copies the elements, so later edits stay local.
• Types that should not be copied silently require an explicit transfer or copy.
• Value semantics makes aliasing visible in the signature.
• Remote or huge buffers can still live behind a pointer inside the value.

Example

def fill(mut items: List[Int]):
    items.append(1)

def main():
    var nums = List[Int]()
    fill(nums)
    print(len(nums))

Keep in mind

If two names must observe the same mutation, pass mut or read instead of copying.