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

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This commit is contained in:
Dave Gauer 2022-08-29 18:30:38 -04:00
parent 93ecc1643e
commit 8da93b5103
2 changed files with 72 additions and 37 deletions
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44
exercises/065_builtins2.zig
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@ -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;
narcissus.me = &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
// use the method syntax (there's no self parameter). Please
// fix this call:
const T2 = narcissus.fetchTheMostBeautifulType();
// this function. We called it as a method, which would work
// if it had a self parameter. But it doesn't. (See above.)
//
// 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..];
}