A simple ring buffer inspired by https://github.com/tsoding/nothing/blob/master/src/ring_buffer.c

ring_buffer.zig

const std = @import("std");

pub fn RingBuffer(comptime T: type) type {
    return struct {
        data: []T,
        current: [*]T,
        count: usize,
        dtor: ?fn (T) void,

        const Self = @This();

        pub fn init(data: []T, dtor: ?fn (T) void) Self {
            return .{ .data = data, .current = data.ptr, .count = 0, .dtor = dtor };
        }

        /// calls dtor() on overwritten element when full
        pub fn push(self: *Self, element: T) void {
            self.current.* = element;
            self.current += 1;

            if (self.count >= self.data.len) {
                if (self.dtor) |dtor| dtor(self.current[0]);
            } else self.count = (self.count + 1) % (self.data.len + 1);
            if (@ptrToInt(self.current) >= @ptrToInt(self.data.ptr + self.data.len))
                self.current = self.data.ptr;
        }

        pub fn pop(self: *Self) ?T {
            if (self.count == 0) return null;
            self.count -= 1;
            self.current -= 1;
            if (@ptrToInt(self.current) < @ptrToInt(self.data.ptr))
                self.current = self.data.ptr + self.data.len - 1;
            return self.current[0];
        }

        pub fn top(self: Self) ?T {
            if (self.count == 0) return null;
            const current = (if (self.current == self.data.ptr)
                self.data.ptr + self.data.len
            else
                self.current) - 1;
            return current[0];
        }
    };
}

test "basic" {
    const assert = std.debug.assert;
    var data = [_]u32{0} ** 5;
    var ring = RingBuffer(u32).init(&data, null);
    var i: u32 = 1;
    assert(ring.pop() == null);
    assert(ring.top() == null);
    while (i < 8) : (i += 1)
        ring.push(i);
    // for (ring.data) |e| std.debug.warn("{}, ", .{e});
    // std.debug.warn("\n", .{});
    assert(ring.data[0] == 6 and ring.data[4] == 5 and ring.top().? == 7);
    i = 1;
    while (i < 5) : (i += 1) {
        const x = ring.pop();
        // std.debug.warn("x={}, top={}\n", .{ x, ring.top() });
    }
    // for (ring.data) |e| std.debug.warn("{}, ", .{e});
    // std.debug.warn("\n", .{});
    assert(ring.top().? == 3);
    i = 1;
    while (i < 7) : (i += 1)
        ring.push(i);
    // for (ring.data) |e| std.debug.warn("{}, ", .{e});
    // std.debug.warn("\n", .{});
    assert(ring.data[0] == 3 and ring.data[4] == 2 and ring.top().? == 6);
}