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Arrays
Tomo supports arrays as a container type that holds a list of elements of any
type in a compact format. Arrays are immutable by default, but use
copy-on-write semantics to efficiently mutate in place when possible. Arrays
are 1-indexed, which means the first item in the array has index 1.
Syntax
Arrays are written using square brackets and a list of comma-separated elements:
nums := [10, 20, 30]
Each element must have the same type (or be easily promoted to the same type). If you want to have an empty array, you must specify what type goes inside the array like this:
empty := [:Int]
For type annotations, an array that holds items with type T is written as [T].
Array Comprehensions
Arrays can also use comprehensions, where you specify how to dynamically create all the elements by iteration instead of manually specifying each:
>> [i*10 for i in 3:to(8)]
= [30, 40, 50, 60, 70, 80]
>> [i*10 for i in 3:to(8) if i != 4]
= [30, 50, 60, 70, 80]
Comprehensions can be combined with regular items or other comprehensions:
>> [-1, i*10 for i in 3:to(8), i for i in 3]
= [-1, 30, 40, 50, 60, 70, 80, 1, 2, 3]
Indexing
Array values are accessed using square bracket indexing. Since arrays are
1-indexed, the index 1 corresponds to the first item in the array. Negative
indices are used to refer to items from the back of the array, so -1 is the
last item, -2 is the second-to-last, and so on.
arr := [10, 20, 30, 40]
>> arr[1]
= 10
>> arr[2]
= 20
>> arr[-1]
= 40
>> arr[-2]
= 30
If an array index of 0 or any value larger than the length of the array is
used, it will trigger a runtime error that will print what the invalid array
index was, the length of the array, and a stack trace. As a performance
operation, if array bounds checking proves to be a performance hot spot, you
can explicitly disable bounds checking by adding arr[i; unchecked] to the
array access.
Iteration
You can iterate over the items in an array like this:
for item in array:
...
for i, item in array:
...
Array iteration operates over the value of the array when the loop began, so modifying the array during iteration is safe and will not result in the loop iterating over any of the new values.
Concatenation
Arrays can be concatenated with the ++ operator, which returns an array that
has the items from one appended to the other. This should not be confused with
the addition operator +, which does not work with arrays.
>> [1, 2] ++ [3, 4]
= [1, 2, 3, 4]
Array Methods
binary_search
Description:
Performs a binary search on a sorted array.
Usage:
binary_search(arr: [T], by=T.compare) -> Int
Parameters:
arr: The sorted array to search.by: The comparison function used to determine order. If not specified, the default comparison function for the item type will be used.
Returns:
Assuming the input array is sorted according to the given comparison function,
return the index where the given item would be inserted to maintain the sorted
order.
Example:
>> [1, 3, 5, 7, 9]:binary_search(5)
= 3
>> [1, 3, 5, 7, 9]:binary_search(-999)
= 1
>> [1, 3, 5, 7, 9]:binary_search(999)
= 6
by
Description:
Creates a new array with elements spaced by the specified step value.
Usage:
by(arr: [T], step: Int) -> [T]
Parameters:
arr: The original array.step: The step value for selecting elements.
Returns:
A new array with every step-th element from the original array.
Example:
>> [1, 2, 3, 4, 5, 6]:by(2)
= [1, 3, 5]
clear
Description:
Clears all elements from the array.
Usage:
clear(arr: & [T]) -> Void
Parameters:
arr: The mutable reference to the array to be cleared.
Returns:
Nothing.
Example:
>> my_array:clear()
counts
Description:
Counts the occurrences of each element in the array.
Usage:
counts(arr: [T]) -> {T: Int}
Parameters:
arr: The array to count elements in.
Returns:
A table mapping each element to its count.
Example:
>> [10, 20, 30, 30, 30]:counts()
= {10: 1, 20: 1, 30: 3}
find
Description:
Finds the index of the first occurrence of an element.
Usage:
find(arr: [T]) -> Int
Parameters:
arr: The array to search through.
Returns:
The index of the first occurrence or -1 if not found.
Example:
>> [10, 20, 30, 40, 50]:find(20)
= 2
>> [10, 20, 30, 40, 50]:find(9999)
= -1
from
Description:
Returns a slice of the array starting from a specified index.
Usage:
from(arr: [T], first: Int) -> [T]
Parameters:
arr: The original array.first: The index to start from.
Returns:
A new array starting from the specified index.
Example:
>> [10, 20, 30, 40, 50]:from(3)
= [30, 40, 50]
has
Description:
Checks if the array has any elements.
Usage:
has(arr: [T]) -> Bool
Parameters:
arr: The array to check.
Returns:
yes if the array has elements, no otherwise.
Example:
>> [10, 20, 30]:has(20)
= yes
heap_pop
Description:
Removes and returns the top element of a heap. By default, this is the
minimum value in the heap.
Usage:
heap_pop(arr: & [T], by=T.compare) -> T
Parameters:
arr: The mutable reference to the heap.by: The comparison function used to determine order. If not specified, the default comparison function for the item type will be used.
Returns:
The removed top element of the heap.
Example:
>> my_heap := [30, 10, 20]
>> my_heap:heapify()
>> my_heap:heap_pop()
= 10
heap_push
Description:
Adds an element to the heap and maintains the heap property. By default, this
is a minimum heap.
Usage:
heap_push(arr: & [T], item: T, by=T.compare) -> Void
Parameters:
arr: The mutable reference to the heap.item: The item to be added.by: The comparison function used to determine order. If not specified, the default comparison function for the item type will be used.
Returns:
Nothing.
Example:
>> my_heap:heap_push(10)
heapify
Description:
Converts an array into a heap.
Usage:
heapify(arr: & [T], by=T.compare) -> Void
Parameters:
arr: The mutable reference to the array to be heapified.by: The comparison function used to determine order. If not specified, the default comparison function for the item type will be used.
Returns:
Nothing.
Example:
>> my_heap := [30, 10, 20]
>> my_heap:heapify()
insert
Description:
Inserts an element at a specified position in the array.
Usage:
insert(arr: & [T], item: T, at: Int = 0) -> Void
Parameters:
arr: The mutable reference to the array.item: The item to be inserted.at: The index at which to insert the item (default is0). Since indices are 1-indexed and negative indices mean "starting from the back", an index of0means "after the last item".
Returns:
Nothing.
Example:
>> arr := [10, 20]
>> arr:insert(30)
>> arr
= [10, 20, 30]
>> arr:insert(999, at=2)
>> arr
= [10, 999, 20, 30]
insert_all
Description:
Inserts an array of items at a specified position in the array.
Usage:
insert_all(arr: & [T], items: [T], at: Int = 0) -> Void
Parameters:
arr: The mutable reference to the array.items: The items to be inserted.at: The index at which to insert the item (default is0). Since indices are 1-indexed and negative indices mean "starting from the back", an index of0means "after the last item".
Returns:
Nothing.
Example:
arr := [10, 20]
arr:insert_all([30, 40])
>> arr
= [10, 20, 30, 40]
arr:insert_all([99, 100], at=2)
>> arr
= [10, 99, 100, 20, 30, 40]
random
Description:
Selects a random element from the array.
Usage:
random(arr: [T]) -> T
Parameters:
arr: The array from which to select a random element.
Returns:
A random element from the array.
Example:
>> [10, 20, 30]:random()
= 20
remove_at
Description:
Removes elements from the array starting at a specified index.
Usage:
remove_at(arr: & [T], at: Int = -1, count: Int = 1) -> Void
Parameters:
arr: The mutable reference to the array.at: The index at which to start removing elements (default is-1, which means the end of the array).count: The number of elements to remove (default is1).
Returns:
Nothing.
Example:
arr := [10, 20, 30, 40, 50]
arr:remove_at(2)
>> arr
= [10, 30, 40, 50]
arr:remove_at(2, count=2)
>> arr
= [10, 50]
remove_item
Description:
Removes all occurrences of a specified item from the array.
Usage:
remove_item(arr: & [T], item: T, max_count: Int = -1) -> Void
Parameters:
arr: The mutable reference to the array.item: The item to be removed.max_count: The maximum number of occurrences to remove (default is-1, meaning all occurrences).
Returns:
Nothing.
Example:
arr := [10, 20, 10, 20, 30]
arr:remove_item(10)
>> arr
= [20, 20, 30]
arr:remove_item(20, max_count=1)
>> arr
= [20, 30]
reversed
Description:
Returns a reversed slice of the array.
Usage:
reversed(arr: [T]) -> [T]
Parameters:
arr: The array to be reversed.
Returns:
A slice of the array with elements in reverse order.
Example:
>> [10, 20, 30]:reversed()
= [30, 20, 10]
sample
Description:
Selects a sample of elements from the array, optionally with weighted
probabilities.
Usage:
sample(arr: [T], count: Int, weights: [Num]) -> [T]
Parameters:
arr: The array to sample from.count: The number of elements to sample.weights: The probability weights for each element in the array. These values do not need to add up to any particular number, they are relative weights. If no weights are provided, the default is equal probabilities. Negative, infinite, or NaN weights will cause a runtime error. If the number of weights given is less than the length of the array, elements from the rest of the array are considered to have zero weight.
Returns:
A list of sampled elements from the array.
Example:
>> [10, 20, 30]:sample(2, weights=[90%, 5%, 5%])
= [10, 10]
shuffle
Description:
Shuffles the elements of the array in place.
Usage:
shuffle(arr: & [T]) -> Void
Parameters:
arr: The mutable reference to the array to be shuffled.
Returns:
Nothing.
Example:
>> arr:shuffle()
shuffled
Description:
Creates a new array with elements shuffled.
Usage:
shuffled(arr: [T]) -> [T]
Parameters:
arr: The array to be shuffled.
Returns:
A new array with shuffled elements.
Example:
>> [10, 20, 30, 40]:shuffled()
= [40, 10, 30, 20]
sort
Description:
Sorts the elements of the array in place in ascending order (small to large).
Usage:
sort(arr: & [T], by=T.compare) -> Void
Parameters:
arr: The mutable reference to the array to be sorted.by: The comparison function used to determine order. If not specified, the default comparison function for the item type will be used.
Returns:
Nothing.
Example:
arr := [40, 10, -30, 20]
arr:sort()
>> arr
= [-30, 10, 20, 40]
arr:sort(func(a,b:&Int): a:abs() <> b:abs())
>> arr
= [10, 20, -30, 40]
sorted
Description:
Creates a new array with elements sorted.
Usage:
sorted(arr: [T], by=T.compare) -> [T]
Parameters:
arr: The array to be sorted.by: The comparison function used to determine order. If not specified, the default comparison function for the item type will be used.
Returns:
A new array with sorted elements.
Example:
>> [40, 10, -30, 20]:sorted()
= [-30, 10, 20, 40]
>> [40, 10, -30, 20]:sorted(func(a,b:&Int): a:abs() <> b:abs())
= [10, 20, -30, 40]
to
Description:
Returns a slice of the array from the start of the original array up to a specified index (inclusive).
Usage:
to(arr: [T], last: Int) -> [T]
Parameters:
arr: The original array.last: The index up to which elements should be included.
Returns:
A new array containing elements from the start up to the specified index.
Example:
>> [10, 20, 30, 40, 50]:to(3)
= [10, 20, 30]
>> [10, 20, 30, 40, 50]:to(-2)
= [10, 20, 30, 40]
unique
Description:
Returns a Set that contains the unique elements of the array.
Usage:
unique(arr: [T]) -> {T}
Parameters:
arr: The array to process.
Returns:
A set containing only unique elements from the array.
Example:
>> [10, 20, 10, 10, 30]:unique()
= {10, 20, 30}