72 lines
1.2 KiB
Markdown
72 lines
1.2 KiB
Markdown
# Function parameters
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## Immutable reference
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```thp
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fun add_25(Array[Int] numbers) {
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numbers.push(25) // Error: `numbers` is immutable
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}
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```
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When using a regular type as a parameter, only it's immutable
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properties can be used inside the function
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```thp
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fun count(Array[Int] numbers) -> Int {
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let items_count = numbers.size() // Ok, `size` is pure
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items_count
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}
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```
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## Mutable reference
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```thp
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fun push_25(mut Array[Int] numbers) {
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numbers.push(25) // Ok, will also mutate the original array
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}
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```
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Placing a `mut` before the type makes the parameter a mutable
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reference. Mutable methods can be used, and the original
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data **can** be mutated.
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The caller *must* also use `mut`.
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```thp
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let numbers = Array(0, 1, 2, 3)
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push_25(mut numbers) // Pass `numbers` as reference.
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print(numbers(4)) // `Some(25)`
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```
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## Clone
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```thp
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fun add_25(clone Array[Int] numbers) {
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numbers.push(25) // Ok, the original array is unaffected
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}
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```
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Using the `clone` keyword before the type creates a mutable copy
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of the parameter (CoW). The original data will **not** be mutated.
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```thp
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let numbers = Array(1, 2, 3, 4)
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add_25(clone numbers) // Pass `numbers` as clone.
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print(numbers(4)) // None
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```
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