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42 lines
No EOL
1.1 KiB
Markdown
42 lines
No EOL
1.1 KiB
Markdown
# Subscript (index access)
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`[]` is different from normal methods.
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```python
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a = [!1, !2]
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a[0].inc!()
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assert a == [2, 2]
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```
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Recall that the return value of a subroutine cannot be a reference.
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The type of `a[0]` here should clearly be `Ref!(Int!)` (the type of `a[0]` depends on the context).
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So `[]` is actually part of a special syntax, just like `.`. Unlike Python, it cannot be overloaded.
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It is also not possible to reproduce the behavior of `[]` in a method.
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```python
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C = Class {i = Int!}
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C. get(ref self) =
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self::i # TypeError: `self::i` is `Int!` (require ownership) but `get` doesn't own `self`
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C.steal(self) =
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self::i
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# NG
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C.new({i = 1}).steal().inc!() # OwnershipWarning: `C.new({i = 1}).steal()` is not owned by anyone
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# hint: assign to a variable or use `uwn_do!`
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# OK (assigning)
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c = C.new({i = 1})
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i = c.steal()
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i.inc!()
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assert i == 2
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# or (own_do!)
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own_do! C.new({i = 1}).steal(), i => i.inc!()
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```
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Also, `[]` can be disowned, but the element is not shifted.
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```python
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a = [!1, !2]
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i = a[0]
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i.inc!()
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assert a[1] == 2
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a[0] # OwnershipError: `a[0]` is moved to `i`
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``` |