Minimal generic stack-based string buffer for zig

strbuff.zig

const std = @import("std");

/// Minimal generic stack-based string buffer
pub fn StrBuff(comptime capacity: usize) type {
    return struct {
        chars: [capacity]u8 = std.mem.zeroes([capacity]u8),
        cur: usize = 0,

        const Error = error{AttemptingToAppendArrayLargerThanCapacity};

        pub fn clear(self: *@This()) void {
            self.chars = std.mem.zeroes([capacity]u8);
            self.cur = 0;
        }

        pub fn len(self: @This()) usize {
            return self.cur;
        }

        pub fn isFull(self: @This()) bool {
            return self.cur >= capacity;
        }

        pub fn append(self: *@This(), string: []const u8) !void {
            if (self.cur + string.len > capacity)
                return Error.AttemptingToAppendArrayLargerThanCapacity;

            const start = self.cur;
            while (self.cur < start + string.len) {
                self.chars[self.cur] = string[self.cur - start];
                self.cur += 1;
            }

            std.log.info("cur: {}", .{self.cur});
        }

        pub fn str(self: @This()) []const u8 {
            return self.chars[0..self.cur];
        }
    };
}

test "append any size" {
    var buff = StrBuff(16){};
    try buff.append("123456789");
    try std.testing.expect(buff.len() == 9);
}

test "append string of exactly capacity size" {
    var buff = StrBuff(8){};
    try buff.append("12345678");
    try std.testing.expect(buff.isFull());
}

test "fail on trying to append huge value" {
    var buff = StrBuff(8){};
    try buff.append("smth");
    try std.testing.expectError(error.AttemptingToAppendArrayLargerThanCapacity, buff.append(" and something really big"));
}

test "multiple appends and clears" {
    var buff = StrBuff(8){};

    try buff.append("1234");
    try buff.append("12");
    buff.clear();

    try buff.append("12345678");

    buff.clear();

    try buff.append("12345");

    buff.clear();

    try std.testing.expect(buff.len() == 1);
}