2021-02-16 20:21:32 -05:00
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//
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// Now that we have optional types, we can apply them to structs.
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// The last time we checked in with our elephants, we had to link
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// all three of them together in a "circle" so that the last tail
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// linked to the first elephant. This is because we had NO CONCEPT
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// of a tail that didn't point to another elephant!
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//
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const std = @import("std"); // single quotes
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const Elephant = struct {
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letter: u8,
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2021-02-28 11:00:20 -05:00
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tail: *Elephant = null, // <---- make this optional!
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2021-02-16 20:21:32 -05:00
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visited: bool = false,
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};
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pub fn main() void {
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var elephantA = Elephant{ .letter = 'A' };
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var elephantB = Elephant{ .letter = 'B' };
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var elephantC = Elephant{ .letter = 'C' };
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// Link the elephants so that each tail "points" to the next.
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elephantA.tail = &elephantB;
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elephantB.tail = &elephantC;
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visitElephants(&elephantA);
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std.debug.print("\n", .{});
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}
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// This function visits all elephants once, starting with the
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// first elephant and following the tails to the next elephant.
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fn visitElephants(first_elephant: *Elephant) void {
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var e = first_elephant;
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while (!e.visited) {
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std.debug.print("Elephant {u}. ", .{e.letter});
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e.visited = true;
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// We should stop once we encounter a tail that
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// does NOT point to another element. What can
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// we put here to make that happen?
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if (e.tail == null) ???;
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e = e.tail.?;
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}
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}
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