80 lines
2.9 KiB
Zig
80 lines
2.9 KiB
Zig
//
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// You've heard of while loops in exercises 011,012,013 and 014
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// You've also heard of switch expressions in exercises 030 and 31.
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// You've also seen how labels can be used in exercise 063.
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//
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// By combining while loops and switch statements with continue and break statements
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// one can create very concise State Machines.
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//
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// One such example would be:
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//
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// pub fn main() void {
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// var op: u8 = 1;
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// while (true) {
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// switch (op) {
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// 1 => { op = 2; continue; },
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// 2 => { op = 3; continue; },
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// 3 => return,
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// 4 => {},
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// }
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// break;
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// }
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// std.debug.print("This statement cannot be reached");
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// }
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//
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// By combining all we've learned so far, we can now proceed with a labeled switch
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//
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// A labeled switch is some extra syntatic sugar, which comes with all sorts of
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// candy (performance benefits). Don't believe me? Directly to source https://github.com/ziglang/zig/pull/21367
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//
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// Here is the previous excerpt implemented as a labeled switch instead:
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//
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// pub fn main() void {
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// foo: switch (@as(u8, 1)) {
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// 1 => continue :foo 2,
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// 2 => continue :foo 3,
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// 3 => return,
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// else => {},
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// }
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// std.debug.print("This statement cannot be reached");
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// }
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//
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// The flow of execution on this second case is:
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// 1. The switch starts with value '1';
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// 2. The switch evaluates to case '1' which in turn uses the continue statement
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// to re-evaluate the labeled switch again, now providing the value '2';
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// 3. In the case '2' we repeat the same pattern as case '1'
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// but instead the value to be evaluated is now '3';
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// 4. Finally we get to case '3', where we return from the function as a whole.
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// 5. In this example as the input has no clear exhaustive patterns but a essentially
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// any u8 integer, we need to handle any case that is not explicitly handled
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// by using the `else => {}` branch as a default case.
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//
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// Since step 4 or a break stament do not exist in this switch, the debug statement is
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// never executed
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//
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const std = @import("std");
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const PullRequestState = enum(u8) {
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Draft,
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InReview,
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Approved,
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Rejected,
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Merged,
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};
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pub fn main() void {
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// Oh no, your pull request keeps being rejected,
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// how would you fix it?
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pr: switch (PullRequestState.Draft) {
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PullRequestState.Draft => continue :pr PullRequestState.InReview,
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PullRequestState.InReview => continue :pr PullRequestState.Rejected,
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PullRequestState.Approved => continue :pr PullRequestState.Merged,
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PullRequestState.Rejected => {
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std.debug.print("The pull request has been rejected.\n", .{});
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return;
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},
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PullRequestState.Merged => break, // Would you know where to break to?
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}
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std.debug.print("The pull request has been merged.\n", .{});
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}
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