Assignment expressions

Assignment operators:

• = and <- (left arrow) are the same assignment in meaning: evaluate the right-hand side and store it in the target (variable, index, or member, where the language allows). The two tokens differ only in syntax—use whichever you prefer for readability or style; there is no separate “mode” in behavior between them.

Omitted object fields in a literal are filled from type defaults (e.g. 0 for int, empty str, etc.), not from whatever was in the variable before. To change only one field, assign to that field:

type Person = {
  name: str,
  age: int,
}

var person: Person = { name: "Alice", age: 30 }
person.name = "Bob"
print(person)

That keeps age: 30 and updates name. By contrast, replacing the whole value with a partial literal overwrites the whole value with a new object where missing fields are defaults:

type Person = {
  name: str,
  age: int,
}

var person: Person = { name: "Alice", age: 30 }
person = { name: "Bob" }
print(person)

You get age: 0 (default for int) and name: "Bob" — not age: 30. The same happens if you write person <- { name: "Bob" }: the operator does not “merge” old field values. To keep age: 30, use a field assignment (first example) or a full new literal, not a partial one.

Fixed-size array example

For Person[2], assigning from an array literal with fewer elements than the fixed size still produces a value of the array type: remaining slots are set from defaults, not the previous array’s elements.

type Person = {
  name: str,
  age: int,
}

var people: Person[2] = [
  { name: "Alice", age: 30 },
  { name: "Bob", age: 30 }
]
people = [{ name: "Charlie", age: 30 }]
print(people)

Typical result: the first entry matches the literal; the second is default-initialized (e.g. empty name, age 0), not the old "Bob" row. You could write people <- [...] here with the same effect.

Notes

• x <- 1 and x = 1, person <- { name: "Bob" } and person = { name: "Bob" } are interchangeable; pick = or <- for taste.
• For partial object or array literals, the same defaulting rules apply: if you need old data preserved, do not rely on a partial literal; update fields explicitly or build a new full value.