Borrow a collection view

A view shares a storage slice without owning its elements. @ creates a read-only view and & a mutable view.

func main() {
    var values = [10, 20, 30, 40, 50]
    {
        let middle = @values[1:4]
        print(middle[0])
    }

    {
        var editable = &values[1:4]
        editable[0] = 42
    }
    print(values[1])
}

Both bounds are required. The start is included and the end excluded. Negative bounds are made relative to count(), then both bounds are clamped to the collection limits.

Accept a view

func sum(values:@int[..]) int {
    var total = 0
    for value in values {
        total += value
    }
    return total
}

Return a view

func identity(values:@int[..]) @values:int[..] {
    return values
}

A view may live in a lexical binding or cross borrowed parameters and returns whose provenance is declared. It owns neither storage nor elements.

Shared and mutable views accept count, is_empty, indexing, subviews, and iteration. A mutable view also accepts indexed writes, for var, and swap. No view can resize, globally reorder, remove, or transfer elements.

A view cannot be stored in an optional, structure, enum, collection, static field, or capture. A slice without @ or & remains an independent copied list.

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