Ranges, arrays and tensors

Ranges, arrays and (in perspective) tensors are container (collection) types for working with sequences and multidimensional data.

Ranges (:Range)

A range is a type, an approximate analog of a “generator” in Python: it alternately yields elements in a given interval with a given step. In the text, a range is specified by two or three elements separated by two dots: 1..5 — from one to five with the default step 1; the step is specified by the third element: 0..10..2. As the boundaries and the step, not only literals but also variables and rational numbers can be used: 0.1..$stop..0.1 — from 0.1 to $stop with step 0.1; 0..100:Rational — a range of rational numbers.

Arrays (:Array)

One-dimensional arrays are supported by the literals [1, 2, 3,] (→ std::vector<Elem>), the constructor :Array(...), access by index a[i] and array methods (count, at, first, push_back, …). Variables with an array type can be created both by value and as reference variables.

The remaining positions of the array can be filled in with the operator ... expr ... (as the last element) — the size is taken from the sized target type: v:Int32[10] := [2, 3, ... 42 ...,]; (see Creating values: filling tensors).

Tensors (:Tensor)

Tensors are multidimensional arrays (based on LibTorch). In the current version multidimensional arrays and full-fledged tensors are not implemented (see Status) — the one-dimensional :Array and the type :Range are implemented.

Indexing

Access to the elements of an array is performed by an integer index starting at 0:

a := [10, 20, 30,];
x := a[0];   # 10

Negative indices (as in Python) are not supported: the reference a[-1] throws a runtime exception. Ranges in the index (a[1..3]), :None values and the ellipsis ... in the index are also not yet implemented.

Iterating over collections

Iterating over the elements of an array, range or dictionary is performed by the loop @while(collection) with destructuring of the current element (a ready example — in the playground; more — Loops).

The standard library provides the iterator type Iterator<T> — a class marked with @[borrowed]. It maps onto C++ trust::AnyIterator<T> (an erased unified cursor) and is available without explicit import (loaded by the prelude; disabled by --no-stdlib). Any variable of the type Iterator<T> is automatically dependent on the source object: use after mutation of the source — the diagnostic -Wborrowed (see Control of reference invalidation). The attribute is inherited by derived types (Iterator<Int32> and others).

Links

• Numbers and tensors
• Dictionaries and sets
• Type conversion
• Type system