Merge branch 'main' into hello_c

This commit is contained in:
Chris Boesch 2023-02-16 11:17:52 +01:00 committed by GitHub
commit dce731a0ec
4 changed files with 136 additions and 1 deletions

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@ -164,7 +164,7 @@ Core Language
* [x] Quoted identifiers @""
* [x] Anonymous structs/tuples/lists
* [ ] Async <--- IN PROGRESS!
* [ ] Interfaces <--- IN PROGRESS!
* [X] Interfaces
* [ ] Working with C
## Contributing

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@ -469,6 +469,10 @@ const exercises = [_]Exercise{
.main_file = "093_hello_c.zig",
.output = "Hello C from Zig! - C result ist 17 chars",
.C = true,
},
.{
.main_file = "092_interfaces.zig",
.output = "Daily Insect Report:\nAnt is alive.\nBee visited 17 flowers.\nGrasshopper hopped 32 meters.",
},
.{
.main_file = "999_the_end.zig",

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@ -0,0 +1,127 @@
//
// Remember our ant and bee simulator constructed with unions
// back in exercises 55 and 56? There, we demonstrated that
// unions allow us to treat different data types in a uniform
// manner.
//
// One neat feature was using tagged unions to create a single
// function to print a status for ants *or* bees by switching:
//
// switch (insect) {
// .still_alive => ... // (print ant stuff)
// .flowers_visited => ... // (print bee stuff)
// }
//
// Well, that simulation was running just fine until a new insect
// arrived in the virtual garden, a grasshopper!
//
// Doctor Zoraptera started to add grasshopper code to the
// program, but then she backed away from her keyboard with an
// angry hissing sound. She had realized that having code for
// each insect in one place and code to print each insect in
// another place was going to become unpleasant to maintain when
// the simulation expanded to hundreds of different insects.
//
// Thankfully, Zig has another comptime feature we can use
// to get out of this dilema called the 'inline else'.
//
// We can replace this redundant code:
//
// switch (thing) {
// .a => |a| special(a),
// .b => |b| normal(b),
// .c => |c| normal(c),
// .d => |d| normal(d),
// .e => |e| normal(e),
// ...
// }
//
// With:
//
// switch (thing) {
// .a => |a| special(a),
// inline else |t| => normal(t),
// }
//
// We can have special handling of some cases and then Zig
// handles the rest of the matches for us.
//
// With this feature, you decide to make an Insect union with a
// single uniform 'print()' function. All of the insects can
// then be responsible for printing themselves. And Doctor
// Zoraptera can calm down and stop gnawing on the furniture.
//
const std = @import("std");
const Ant = struct {
still_alive: bool,
pub fn print(self: Ant) void {
std.debug.print("Ant is {s}.\n", .{if (self.still_alive) "alive" else "dead"});
}
};
const Bee = struct {
flowers_visited: u16,
pub fn print(self: Bee) void {
std.debug.print("Bee visited {} flowers.\n", .{self.flowers_visited});
}
};
// Here's the new grasshopper. Notice how we've also added print
// methods to each insect.
const Grasshopper = struct {
distance_hopped: u16,
pub fn print(self: Grasshopper) void {
std.debug.print("Grasshopper hopped {} meters.\n", .{self.distance_hopped});
}
};
const Insect = union(enum) {
ant: Ant,
bee: Bee,
grasshopper: Grasshopper,
// Thanks to 'inline else', we can think of this print() as
// being an interface method. Any member of this union with
// with a print() method can be treated uniformly by outside
// code without needing to know any other details. Cool!
pub fn print(self: Insect) void {
switch (self) {
inline else => |case| return case.print(),
}
}
};
pub fn main() !void {
var my_insects = [_]Insect{
Insect{ .ant = Ant{ .still_alive = true } },
Insect{ .bee = Bee{ .flowers_visited = 17 } },
Insect{ .grasshopper = Grasshopper{ .distance_hopped = 32 }, },
};
std.debug.print("Daily Insect Report:\n", .{});
for (my_insects) |insect| {
// Almost done! We want to print() each insect with a
// single method call here.
???
}
}
// Our print() method in the Insect union above demonstrates
// something very similar to the object-oriented concept of an
// abstract data type. That is, the Insect type doesn't contain
// the underlying data, and the print() function doesn't
// actually do the printing.
//
// The point of an interface is to support generic programming:
// the ability to treat different things as if they were the
// same to cut down on clutter and conceptual complexity.
//
// The Daily Insect Report doesn't need to worry about *which*
// insects are in the report - they all print the same way via
// the interface!
//
// Doctor Zoraptera loves it.

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@ -0,0 +1,4 @@
109c109
< ???
---
> insect.print();