my ziglings
Correct conventional Zig reference vs value passing re #89
Dave Gauer
(Jul 31, 2022, 3:58 PM EDT)
dee6a96d
18c761d8
+49
-19
+2
-1
build.zig
+2
-1
build.zig
+10
-1
exercises/042_pointers4.zig
+10
-1
exercises/042_pointers4.zig
···
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//
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// Now let's use pointers to do something we haven't been
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// able to do before: pass a value by reference to a function!
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// able to do before: pass a value by reference to a function.
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//
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// Why would we wish to pass a pointer to an integer variable
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// rather than the integer value itself? Because then we are
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// allowed to *change* the value of the variable!
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//
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// +-----------------------------------------------+
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// | Pass by reference when you want to change the |
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// | pointed-to value. Otherwise, pass the value. |
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// +-----------------------------------------------+
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//
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const std = @import("std");
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+29
-11
exercises/043_pointers5.zig
+29
-11
exercises/043_pointers5.zig
···
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//
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// Passing integer pointers around is generally not something you're going
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// to do. Integers are cheap to copy.
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//
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// But you know what IS useful? Pointers to structs:
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// As with integers, you can pass a pointer to a struct when you
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// will wish to modify that struct. Pointers are also useful when
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// you need to store a reference to a struct (a "link" to it).
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//
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// const Vertex = struct{ x: u32, y: u32, z: u32 };
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//
···
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// YES: pv.x
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// NO: pv.*.x
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//
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// We can write functions that take pointer arguments:
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// We can write functions that take pointers to structs as
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// arguments. This foo() function modifies struct v:
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//
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// fn foo(v: *Vertex) void {
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// v.x += 2;
···
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// v.z += 7;
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// }
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//
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// And pass references to them:
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// And call them like so:
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//
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// foo(&v1);
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//
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//
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// Let's revisit our RPG example and make a printCharacter() function
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// that takes a Character pointer.
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// that takes a Character by reference and prints it...*and*
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// prints a linked "mentor" Character, if there is one.
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//
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const std = @import("std");
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···
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const Character = struct {
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class: Class,
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gold: u32,
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health: u8 = 100, // <--- You can also provide fields a default value!
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health: u8 = 100, // You can provide default values
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experience: u32,
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+
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// I need to use the '?' here to allow for a null value. But
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// I don't explain it until later. Please don't tell anyone.
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mentor: ?*Character = null,
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};
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pub fn main() void {
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var glorp = Character{
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var mighty_krodor = Character{
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.class = Class.wizard,
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.gold = 10000,
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.experience = 2340,
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};
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+
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var glorp = Character{ // Glorp!
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.class = Class.wizard,
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.gold = 10,
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.experience = 20,
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.mentor = &mighty_krodor, // Glorp's mentor is the Mighty Krodor
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};
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// FIX ME!
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// Please pass our Character "glorp" to printCharacter():
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// Please pass Glorp to printCharacter():
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printCharacter(???);
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}
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···
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c.health,
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c.experience,
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});
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+
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// Checking an "optional" value and capturing it will be
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// explained later (this pairs with the '?' mentioned above.)
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if (c.mentor) |mentor| {
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std.debug.print(" Mentor: ", .{});
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printCharacter(mentor);
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}
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}
+3
-3
exercises/047_methods.zig
+3
-3
exercises/047_methods.zig
···
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// pub fn hello() void {
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// std.debug.print("Foo says hello!\n", .{});
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// }
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// }
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// };
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//
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// 2. A function that is a member of a struct is a "method" and is
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// called with the "dot syntax" like so:
···
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// const Bar = struct{
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// number: u32,
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//
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// pub fn printMe(self: *Bar) void {
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// pub fn printMe(self: Bar) void {
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// std.debug.print("{}\n", .{self.number});
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// }
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// }
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// };
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//
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// (Actually, you can name the first parameter anything, but
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// please follow convention and use "self".)
+3
-1
patches/gollum.sh
+3
-1
patches/gollum.sh
···
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if [ ! -f $b ]; then echo "No $f! We hates it!"; exit 1; fi
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if [ ! -f $a ]; then echo "No $a! Where is it? Where is the answer, precious?"; exit; fi
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echo "Hissss!\tbefore: '$b'\n\t after: '$a'\n\t patch: '$p'\n"
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echo "Hissss! before: '$b'"
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echo " after: '$a'"
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echo " patch: '$p'"
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diff $b $a > $p
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+1
-1
patches/patches/042_pointers4.patch
+1
-1
patches/patches/042_pointers4.patch