Ex 065: improve hints, fix type printing change. For #120 and #128

exercises/065_builtins2.zig

@@ -40,12 +40,12 @@
 // (Notice how the two functions which return types start with
 // uppercase letters? This is a standard naming practice in Zig.)
 //
-const print = import(std).debug.print; // Oops!
+const print = @import("std").debug.print;
 
 const Narcissus = struct {
     me: *Narcissus = undefined,
     myself: *Narcissus = undefined,
-    echo: void = undefined,
+    echo: void = undefined, // Alas, poor Echo!
 
     fn fetchTheMostBeautifulType() type {
         return @This();
@@ -57,20 +57,26 @@ pub fn main() void {
 
     // Oops! We cannot leave the 'me' and 'myself' fields
     // undefined. Please set them here:
-    ??? = &narcissus;
+    narcissus.me = &narcissus;
-    ??? = &narcissus;
+    narcissus.??? = ???;
 
     // This determines a "peer type" from three separate
     // references (they just happen to all be the same object).
-    const T1 = @TypeOf(narcissus, narcissus.me.*, narcissus.myself.*);
+    const Type1 = @TypeOf(narcissus, narcissus.me.*, narcissus.myself.*);
 
     // Oh dear, we seem to have done something wrong when calling
-    // this function. It is namespaced to the struct, but doesn't
+    // this function. We called it as a method, which would work
-    // use the method syntax (there's no self parameter). Please
+    // if it had a self parameter. But it doesn't. (See above.)
-    // fix this call:
+    //
-    const T2 = narcissus.fetchTheMostBeautifulType();
+    // The fix for this is very subtle, but it makes a big
+    // difference!
+    const Type2 = narcissus.fetchTheMostBeautifulType();
 
-    print("A {} loves all {}es. ", .{ T1, T2 });
+    // Now we print a pithy statement about Narcissus.
+    print("A {s} loves all {s}es. ", .{
+        maximumNarcissism(Type1),
+        maximumNarcissism(Type2),
+    });
 
     //   His final words as he was looking in
     //   those waters he habitually watched
@@ -121,7 +127,23 @@ pub fn main() void {
     // Alas, we can't use a regular 'for' loop here because
     // 'fields' can only be evaluated at compile time.  It seems
     // like we're overdue to learn about this "comptime" stuff,
-    // doesn't it? :-)
+    // doesn't it? Don't worry, we'll get there.
 
     print(".\n", .{});
 }
+
+// NOTE: This exercise did not originally include the function below.
+// But a change after Zig 0.10.0 added the source file name to the
+// type. "Narcissus" became "065_builtins2.Narcissus".
+//
+// To fix this, I've added this function to strip the filename from
+// the front of the type name in the dumbest way possible. (It returns
+// a slice of the type name starting at character 14 (assuming
+// single-byte characters).
+//
+// We'll be seeing @typeName again in Exercise 070. For now, you can
+// see that it takes a Type and returns a u8 "string".
+fn maximumNarcissism(myType: anytype) []const u8 {
+    // Turn '065_builtins2.Narcissus' into 'Narcissus'
+    return @typeName(myType)[14..];
+}

patches/patches/065_builtins2.patch

@@ -1,26 +1,39 @@
-43c43
+--- exercises/065_builtins2.zig
-< const print = import(std).debug.print; // Oops!
++++ answers/065_builtins2.zig
----
+@@ -58,7 +58,7 @@
-> const print = @import("std").debug.print;
+     // Oops! We cannot leave the 'me' and 'myself' fields
-60,61c60,61
+     // undefined. Please set them here:
-<     ??? = &narcissus;
+     narcissus.me = &narcissus;
-<     ??? = &narcissus;
+-    narcissus.??? = ???;
----
++    narcissus.myself = &narcissus;
->     narcissus.me = &narcissus;
+ 
->     narcissus.myself = &narcissus;
+     // This determines a "peer type" from three separate
-71c71
+     // references (they just happen to all be the same object).
-<     const T2 = narcissus.fetchTheMostBeautifulType();
+@@ -70,7 +70,7 @@
----
+     //
->     const T2 = Narcissus.fetchTheMostBeautifulType();
+     // The fix for this is very subtle, but it makes a big
-106c106
+     // difference!
-<     if (fields[0].??? != void) {
+-    const Type2 = narcissus.fetchTheMostBeautifulType();
----
++    const Type2 = Narcissus.fetchTheMostBeautifulType();
->     if (fields[0].field_type != void) {
+ 
-110c110
+     // Now we print a pithy statement about Narcissus.
-<     if (fields[1].??? != void) {
+     print("A {s} loves all {s}es. ", .{
----
+@@ -109,15 +109,15 @@
->     if (fields[1].field_type != void) {
+     // Please complete these 'if' statements so that the field
-114c114
+     // name will not be printed if the field is of type 'void'
-<     if (fields[2].??? != void) {
+     // (which is a zero-bit type that takes up no space at all!):
----
+-    if (fields[0].??? != void) {
->     if (fields[2].field_type != void) {
++    if (fields[0].field_type != void) {
+         print(" {s}", .{@typeInfo(Narcissus).Struct.fields[0].name});
+     }
+ 
+-    if (fields[1].??? != void) {
++    if (fields[1].field_type != void) {
+         print(" {s}", .{@typeInfo(Narcissus).Struct.fields[1].name});
+     }
+ 
+-    if (fields[2].??? != void) {
++    if (fields[2].field_type != void) {
+         print(" {s}", .{@typeInfo(Narcissus).Struct.fields[2].name});
+     }
+