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Fix 076, add 077,078 sentinels and many-item pointers

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This commit is contained in:
Dave Gauer 2021-05-08 18:51:08 -04:00
parent 71e43b0a50
commit 22ac3628a1
7 changed files with 126 additions and 35 deletions
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46
exercises/076_sentinels.zig
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@ -29,11 +29,11 @@
// Slice 'b' is only allowed to point to zero-terminated arrays
// but otherwise works just like a normal slice.
//
// Pointer 'c' is exactly like the many-pointers we learned about
// in exercise 054, but it is guaranteed to end in 0. Because of
// this guarantee, we can safely find the end of this
// many-pointer without knowing its length. (We CAN'T do that
// with regular many-pointers!).
// Pointer 'c' is exactly like the many-item pointers we learned
// about in exercise 054, but it is guaranteed to end in 0.
// Because of this guarantee, we can safely find the end of this
// many-item pointer without knowing its length. (We CAN'T do
// that with regular many-item pointers!).
//
const print = @import("std").debug.print;
@ -41,24 +41,25 @@ pub fn main() void {
// Here's a zero-terminated array of u32 values:
var nums = [_:0]u32{ 1, 2, 3, 4, 5, 6 };
// And here's a zero-terminated many-pointer:
// And here's a zero-terminated many-item pointer:
var ptr: [*:0]u32 = &nums;
// For fun, let's replace the value at position 3 with the
// sentinel value 0. This seems kind of naughty.
nums[3] = 0;
// So now we have a zero-terminated array and a many-pointer
// that reference the same data: a sequence of numbers that
// both ends in and CONTAINS the sentinal value.
// So now we have a zero-terminated array and a many-item
// pointer that reference the same data: a sequence of
// numbers that both ends in and CONTAINS the sentinal value.
//
// Attempting to loop through and print both of these should
// demonstrate how they are similar and different.
//
// (It turns out that the array prints completely, including
// the sentinel 0 in the middle. The many-pointer must stop
// at the first sentinel value. The difference is simply that
// arrays have a known length and many-pointers don't.)
// the sentinel 0 in the middle. The many-item pointer must
// stop at the first sentinel value. The difference is simply
// that arrays have a known length and many-item pointers
// don't.)
printSequence(nums);
printSequence(ptr);
@ -86,7 +87,7 @@ fn printSequence(my_seq: anytype) void {
.Pointer => {
// Check this out - it's pretty cool:
const my_sentinel = my_type.Pointer.sentinel;
print("Many-pointer:", .{});
print("Many-item pointer:", .{});
// Loop through the items in my_seq until we hit the
// sentinel value.
@ -100,22 +101,3 @@ fn printSequence(my_seq: anytype) void {
}
print(". ", .{});
}
//
// ------------------------------------------------------------
// TOP SECRET TOP SECRET TOP SECRET TOP SECRET TOP SECRET
// ------------------------------------------------------------
//
// Are you ready for the THE TRUTH about Zig string literals?
//
// You've earned it. Here it is:
//
// @TypeOf("foo") == *const [3:0]u8
//
// Zig's string literals are constant pointers to zero-terminated
// (or "null-terminated") arrays of u8.
//
// Now you know. Welcome to the secret club!
//
// ------------------------------------------------------------
// TOP SECRET TOP SECRET TOP SECRET TOP SECRET TOP SECRET
// ------------------------------------------------------------