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+//
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+// Zig has builtins for mathematical operations such as...
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+//
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+// @sqrt @sin @cos
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+// @exp @log @floor
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+//
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+// ...and lots of type casting operations such as...
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+//
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+// @as @intToError @intToFloat
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+// @intToPtr @ptrToInt @enumToInt
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+//
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+// Spending part of a rainy day skimming through the complete
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+// list of builtins in the official Zig documentation wouldn't be
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+// a bad use of your time. There are some seriously cool features
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+// in there. Check out @call, @compileLog, @embedFile, and @src!
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+//
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+// ...
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+//
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+// For now, we're going to complete our examination of builtins
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+// by exploring just THREE of Zig's MANY introspection abilities:
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+//
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+// 1. @This() type
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+//
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+// Returns the innermost struct, enum, or union that a function
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+// call is inside.
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+//
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+// 2. @typeInfo(comptime T: type) @import("std").builtin.TypeInfo
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+//
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+// Returns information about any type in a TypeInfo union which
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+// will contain different information depending on which type
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+// you're examining.
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+//
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+// 3. @TypeOf(...) type
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+//
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+// Returns the type common to all input parameters (each of which
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+// may be any expression). The type is resolved using the same
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+// "peer type resolution" process the compiler itself uses when
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+// inferring types.
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+//
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+// (Notice how the two functions which return types start with
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+// uppercase letters? This is a standard naming practice in Zig.)
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+//
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+const print = import(std).debug.print; // Oops!
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+
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+const Narcissus = struct {
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+ me: *Narcissus = undefined,
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+ myself: *Narcissus = undefined,
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+ echo: void = undefined,
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+
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+ fn fetchTheMostBeautifulType() type {
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+ return @This();
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+ }
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+};
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+
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+pub fn main() void {
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+ var narcissus: Narcissus = Narcissus {};
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+
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+ // Oops! We cannot leave the 'me' and 'myself' fields
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+ // undefined. Please set them here:
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+ ??? = &narcissus;
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+ ??? = &narcissus;
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+
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+ // This determines a "peer type" from three separate
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+ // references (they just happen to all be the same object).
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+ const T1 = @TypeOf(narcissus, narcissus.me.*, narcissus.myself.*);
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+
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+ // Oh dear, we seem to have done something wrong when calling
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+ // this function. It is namespaced to the struct, but doesn't
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+ // use the method syntax (there's no self parameter). Please
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+ // fix this call:
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+ const T2 = narcissus.fetchTheMostBeautifulType();
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+
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+ print("A {} loves all {}es. ", .{T1, T2});
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+
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+ // His final words as he was looking in
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+ // those waters he habitually watched
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+ // were these:
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+ // "Alas, my beloved boy, in vain!"
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+ // The place gave every word back in reply.
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+ // He cried:
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+ // "Farewell."
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+ // And Echo called:
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+ // "Farewell!"
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+ //
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+ // --Ovid, The Metamorphoses
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+ // translated by Ian Johnston
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+
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+ print("He has room in his heart for:", .{});
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+
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+ // A StructFields array
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+ const fields = @typeInfo(Narcissus).Struct.fields;
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+
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+ // 'fields' is an array of StructFields. Here's the declaration:
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+ //
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+ // pub const StructField = struct {
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+ // name: []const u8,
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+ // field_type: type,
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+ // default_value: anytype,
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+ // is_comptime: bool,
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+ // alignment: comptime_int,
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+ // };
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+ //
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+ // Please complete these 'if' statements so that the field
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+ // name will not be printed if the field is of type 'void'
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+ // (which is a zero-bit type that takes up no space at all!):
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+ if (fields[0].??? != void) {
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+ print(" {s}", .{@typeInfo(Narcissus).Struct.fields[0].name});
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+ }
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+
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+ if (fields[1].??? != void) {
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+ print(" {s}", .{@typeInfo(Narcissus).Struct.fields[1].name});
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+ }
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+
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+ if (fields[2].??? != void) {
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+ print(" {s}", .{@typeInfo(Narcissus).Struct.fields[2].name});
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+ }
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+
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+ // Yuck, look at all that repeated code above! I don't know
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+ // about you, but it makes me itchy.
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+ //
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+ // Alas, we can't use a regular 'for' loop here because
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+ // 'fields' can only be evaluated at compile time. It seems
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+ // like we're overdue to learn about this "comptime" stuff,
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+ // isn't it? :-)
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+
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+ print(".\n", .{});
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+}
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Dave Gauer