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doc: improve array docs (#5950)

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Nick Treleaven 2020-07-26 19:29:51 +01:00 committed by GitHub
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@ -446,23 +446,21 @@ println(nums.len) // "0"
// Declare an empty array: // Declare an empty array:
users := []int{} users := []int{}
// We can also preallocate a certain amount of elements.
ids := []int{ len: 50, init: 0 } // This creates an array with 50 zeros
``` ```
The type of an array is determined by the first element: The type of an array is determined by the first element:
* `[1, 2, 3]` is an array of ints (`[]int`). * `[1, 2, 3]` is an array of ints (`[]int`).
* `['a', 'b']` is an array of strings (`[]string`). * `['a', 'b']` is an array of strings (`[]string`).
If V is unable to infer the type of an array, the user can explicitly specify it for the first element: `[byte(0x0E), 0x1F, 0xBA, 0x0E]` If V is unable to infer the type of an array, the user can explicitly specify it for the first element: `[byte(16), 32, 64, 128]`.
V arrays are homogeneous (all elements must have the same type). This means that code like `[1, 'a']` will not compile. V arrays are homogeneous (all elements must have the same type). This means that code like `[1, 'a']` will not compile.
`.len` field returns the length of the array. Note that it's a read-only field, The `.len` field returns the length of the array. Note that it's a read-only field,
and it can't be modified by the user. Exported fields are read-only by default in V. and it can't be modified by the user. Exported fields are read-only by default in V.
See [Access modifiers](#access-modifiers). See [Access modifiers](#access-modifiers).
#### Array operations
```v ```v
mut nums := [1, 2, 3] mut nums := [1, 2, 3]
nums << 4 nums << 4
@ -485,26 +483,26 @@ It can also append an entire array.
`val in array` returns true if the array contains `val`. See [`in` operator](#in-operator). `val in array` returns true if the array contains `val`. See [`in` operator](#in-operator).
&nbsp; #### Initializing array properties
During initialization you can specify the capacity of the array (`cap`), its initial length (`len`), During initialization you can specify the capacity of the array (`cap`), its initial length (`len`),
and the default element (`init`). and the default element (`init`):
Setting the capacity improves performance of insertions, as it reduces the amount of reallocations in ```v
dynamic arrays: arr := []int{ len: 5, init: -1 } // `[-1, -1, -1, -1, -1]`
```
Setting the capacity improves performance of insertions, as it reduces the number of reallocations needed:
```v ```v
mut numbers := []int{ cap: 1000 } mut numbers := []int{ cap: 1000 }
// Now able to add new elements without reallocating println(numbers.len) // 0
// Now appending elements won't reallocate
for i in 0 .. 1000 { for i in 0 .. 1000 {
numbers << i numbers << i
// same as
// numbers[i] = i
} }
``` ```
Note: The above code uses a [range `for`](#range-for) statement.
`[]int{ len: 5, init: -1 }` will create `[-1, -1, -1, -1, -1]`.
#### Array methods #### Array methods