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The first exercise introduces the `packed` keyword as an alternative for bitwise operations. Its main goals are establishing a solid understanding of field order and conveying the fact that packed containers are basically integers. It introduces the concept of container layouts and briefly explains the default `auto` layout before introducing the `packed` layout (but doesn't touch `extern` at all). The exercise also presents a real-world use case for packed containers, namely LZ4 frame descriptors. Furthermore it covers equality comparisons between packed containers. The second exercise talks about switch statements with packed containers and goes into some more detail on packed unions.
33 lines
998 B
Diff
33 lines
998 B
Diff
--- exercises/112_packed2.zig 2026-03-13 11:14:08
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+++ answers/112_packed2.zig 2026-03-13 11:14:16
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@@ -13,9 +13,9 @@
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const s: S = .{ .a = true, .b = -1 };
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switch (s) {
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.{ .a = true, .b = -1 } => {}, // ok!
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- .{ .a = true, .b = ??? },
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- .{ .a = ???, .b = 0 },
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- .{ .a = ???, .b = ??? },
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+ .{ .a = true, .b = 0 },
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+ .{ .a = false, .b = 0 },
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+ .{ .a = false, .b = -1 },
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=> @compileError("We don't want to end up here!"),
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}
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}
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@@ -39,7 +39,6 @@
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.{ .a = 3 } => {}, // ok!
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.{ .a = 2 },
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.{ .b = 1 },
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- .{ .b = -1 },
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.{ .a = 0 },
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=> @compileError("We don't want to end up here!"),
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}
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@@ -65,7 +64,7 @@
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// Reminder: if the sign bit of a float is set, the number is negative!
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var number: Float = .{ .value = 2.34 };
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- number.bits.??? = ???;
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+ number.bits.sign = 1;
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if (number.value != -2.34) {
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std.debug.print("Make it negative!\n", .{});
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}
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