Span views in Mojo

A Span borrows a window into a list without copying any of it.

def total(values: Span[Int, _]) -> Int:
    var sum = 0
    for value in values:
        sum += value
    return sum


def main():
    var samples = [3, 1, 4, 1, 5, 9, 2, 6]
    print(total(Span(samples)))
    print(total(Span(samples)[2:5]))
    var window = Span(samples)[0:3]
    window[0] = 100
    print(samples[0])

How it works

1. Span[Int, _] leaves the origin unbound, so any list can be passed.
2. Slicing a span narrows the window to a sub-range.
3. Writing through the span mutates the original list.

Keywords and builtins used here

• Int
• def
• for
• main
• print
• return
• sum
• total
• var

The run, in numbers

Lines

14

Characters to type

276

Tokens

96

Three-star pace

70 tpm

At the three-star pace of 70 tokens a minute, this run takes about 82 seconds.

Type this snippet

Step 4 of 4 in Memory, step 20 of 22 in Parameters & SIMD.

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