Returning multiple values

We can return more than one value at once from a function in two ways:

By returning an array if the values are of the same type
By using anonymous structs

In the following example, we are tasked with building a mechanism to carry water from the river up to the castle, which is 90 meters high! As the best Renaissance engineer at court, we devise a tower that, thanks to an ingenious system of oscillating buckets, is capable of lifting water up to 4.5 meters high:

hydrotower.zig

const std = @import("std");

const print = std.debug.print;

// a tower with oscillating buckets

const HydroTower = struct {

// typical percentage of water that can be

// carried per meter of height gained

const N_EFFICIENCY_PER_METER: f32 = 0.98;

// tower height

n_height: f32,

n_efficiency_per_meter: ?f32, // optional

// the tower lifts the incoming water

// and returns how much arrives and at what height

fn lift_water(self: *const HydroTower, n_input: f32) [2]f32 {

return .{

n_input * std.math.pow(

f32,

// if we do not set a specific efficiency

// for the tower, the typical one is used

self.n_efficiency_per_meter orelse

HydroTower.N_EFFICIENCY_PER_METER,

self.n_height,

};

}

};

// river flow carried to the tower

const WaterFlow = struct {

n_liters_per_second: f32,

};

pub fn main() void {

print("~\n", .{});

// flow of 2L per second

const o_river = WaterFlow{ .n_liters_per_second = 2 };

// tower built with a height of 4.5m

const o_tower = HydroTower{

.n_height = 4.5,

// no specific efficiency is set

.n_efficiency_per_meter = null,

};

// destructure the returned array

const n_water, const n_height = o_tower

.lift_water(o_river.n_liters_per_second);

print("{}L → {}L at {}m \n", .{ o_river.n_liters_per_second, n_water, n_height });

}

$ zig run hydrotower.zig

2L → 1.826196L at 4.5m

The lift_water method returns multiple values using an array:

[2]f32 { // <- it will return an array with 2 float elements

//...

// destructure the returned array

const n_water, const n_height = o_tower

.lift_water(o_river.n_liters_per_second);