add ex069 comptime 4

1 files changed, 54 insertions, 0 deletions

diff --git a/exercises/069_comptime4.zig b/exercises/069_comptime4.zig
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+//
+// One of the more common uses of 'comptime' function parameters is
+// passing a type to a function:
+//
+//     fn foo(comptime MyType: type) { ... }
+//
+// In fact, types are ONLY available at compile time, so the
+// 'comptime' keyword is required here.
+//
+// Please take a moment put on the wizard hat which has been
+// provided for you. We're about to use this ability to implement
+// a generic function.
+//
+const print = @import("std").debug.print;
+
+pub fn main() void  {
+    // Here we declare arrays of three different types and sizes
+    // at compile time from a function call. Neat!
+    const s1 = makeSequence(u8, 3);  // creates a [3]u8
+    const s2 = makeSequence(u32, 5); // creates a [5]u32
+    const s3 = makeSequence(i64, 7); // creates a [7]i64
+
+    print("s1={any}, s2={any}, s3={any}\n", .{s1, s2, s3});
+}
+
+// This function is pretty wild because it executes at runtime
+// and is part of the final compiled program. The function is
+// compiled with unchanging data sizes and types.
+//
+// And yet it ALSO allows for different sizes and types. This
+// seems paradoxical. How could both things be true?
+//
+// To accomplish this, the Zig compiler actually generates a
+// separate copy of the function for every size/type combination!
+// So in this case, three different functions will be generated
+// for you, each with machine code that handles that specific
+// data size and type.
+//
+// Please fix this function so that the 'size' parameter:
+//
+//     1) Is guaranteed to be known at compile time.
+//     2) Sets the size of the array of type T (which is the
+//        sequence we're creating and returning).
+//
+fn makeSequence(comptime T: type, ??? size: usize) [???]T {
+    var sequence: [???]T = undefined;
+    var i: usize = 0;
+
+    while (i < size) : (i += 1) {
+        sequence[i] = @intCast(T, i) + 1;
+    }
+    
+    return sequence;
+}