Multiple associated values for an enum

Help
1

Hi Friends.

I’m having trouble building a data structure. I’m writing a parser, and interpreter in Zig. I want to use a value of an enum as the key for a fixed size, static, hashMap, or array of values. The enum represents tokens: Token.Type, and the data structure represents an array of parsing rules. In C this would look like this:

ParseRule rules[] = {
  [TOKEN_LEFT_PAREN]    = {grouping, call,   PREC_CALL},
  [TOKEN_RIGHT_PAREN]   = {NULL,     NULL,   PREC_NONE},
  [TOKEN_LEFT_BRACE]    = {NULL,     NULL,   PREC_NONE}, // [big]
  [TOKEN_RIGHT_BRACE]   = {NULL,     NULL,   PREC_NONE},
  // .. Truncated for brevity.
  [TOKEN_EOF]           = {NULL,     NULL,   PREC_NONE},
};

I feel like I’m almost there, but can’t seem to find a way to map this sort of structure to Zig.

Any help would be greatly appreciated.

-kow

2

Hi, you probably need std.EnumMap.

FYI, there’re also std.EnumSet and std.EnumArray, and even more things in std.enums namespace.

4 Likes
3

Awesome! This is exactly what I was looking for. Perhaps I should look through the standard library first next time.

Thanks again.

-kow

2 Likes
4

I also started to use the same solution in my current project.
But this issue EnumMap is unusable for enums with many fields… raised my attention :joy:

5

With Zig 0.14.1, I use std.enums.directEnumArray for this part of the Crafting Interpreters book, see here:

As a side note, as others have mentioned in reviews, if you use a different language instead of C, or if you try the challenges, it becomes increasingly difficult in later chapters to see where to change the code, because the author usually shows one or two lines of context.
I recommend to not try the challenges, or at least not in your main branch.

Don’t take my code for Zig best practice, I’m a newbie in Zig. Probably there are more elegant solutions.

6

@setEvalBranchQuota can be a workaround.

7

I am still screaming for direct access in the language.
(no complications with “holes” just using maxvalue for the length).

const Enum = enum { one, two, three };
var enums: [Enum]u64 = undefined;
enums[.one] = 42;
enums[.two] = 43;
enums[.three] = 44;
8

Just use something like this and add 1 to it, to get the length for a dense array:

Or use std.enums.directEnumArrayLen

Ahh ok, you want array indexing directly via enums.

1 Like
9

@setEvalBranchQuota(9999999) - is the part of the issue:

Steps to Reproduce …

Reproduction:

const std = @import("std");
pub const SystemErrno = enum(u8) {
    E2BIG = 7,
    EACCES = 13,
    EADDRINUSE = 100,
    EADDRNOTAVAIL = 101,
    EAFNOSUPPORT = 102,
    EAGAIN = 11,
    EALREADY = 103,
    EBADF = 9,
    EBADMSG = 104,
    EBUSY = 16,
    ECANCELED = 105,
    ECHILD = 10,
    ECONNABORTED = 106,
    ECONNREFUSED = 107,
    ECONNRESET = 108,
    EDEADLOCK = 36,
    EDESTADDRREQ = 109,
    EDOM = 33,
    EEXIST = 17,
    EFAULT = 14,
    EFBIG = 27,
    EHOSTUNREACH = 110,
    EIDRM = 111,
    EILSEQ = 42,
    EINPROGRESS = 112,
    EINTR = 4,
    EINVAL = 22,
    EIO = 5,
    EISCONN = 113,
    EISDIR = 21,
    ELOOP = 114,
    EMFILE = 24,
    EMLINK = 31,
    EMSGSIZE = 115,
    ENAMETOOLONG = 38,
    ENETDOWN = 116,
    ENETRESET = 117,
    ENETUNREACH = 118,
    ENFILE = 23,
    ENOBUFS = 119,
    ENODATA = 120,
    ENODEV = 19,
    ENOENT = 2,
    ENOEXEC = 8,
    ENOLCK = 39,
    ENOLINK = 121,
    ENOMEM = 12,
    ENOMSG = 122,
    ENOPROTOOPT = 123,
    ENOSPC = 28,
    ENOSR = 124,
    ENOSTR = 125,
    ENOSYS = 40,
    ENOTCONN = 126,
    ENOTDIR = 20,
    ENOTEMPTY = 41,
    ENOTRECOVERABLE = 127,
    ENOTSOCK = 128,
    ENOTSUP = 129,
    ENOTTY = 25,
    ENXIO = 6,
    EOPNOTSUPP = 130,
    EOTHER = 131,
    EOVERFLOW = 132,
    EOWNERDEAD = 133,
    EPERM = 1,
    EPIPE = 32,
    EPROTO = 134,
    EPROTONOSUPPORT = 135,
    EPROTOTYPE = 136,
    ERANGE = 34,
    EROFS = 30,
    ESPIPE = 29,
    ESRCH = 3,
    ETIME = 137,
    ETIMEDOUT = 138,
    ETXTBSY = 139,
    EWOULDBLOCK = 140,
    EXDEV = 18,
    STRUNCATE = 80,

    pub const max = @intFromEnum(SystemErrno.EWOULDBLOCK);

    pub const labels: std.EnumMap(SystemErrno, []const u8) = brk: {
        @setEvalBranchQuota(9999999);  <=====
        var labels_ = std.EnumMap(SystemErrno, []const u8).init(.{
            .E2BIG = "Argument list too long",
            .EACCES = "Permission denied. The file's permission setting doesn't allow the specified access. An attempt was made to access a file (or, in some cases, a directory) in a way that's incompatible with the file's attributes",
            .EADDRINUSE = "Address in use",
            .EADDRNOTAVAIL = "Address not available",
            .EAFNOSUPPORT = "Address family not supported",
            .EALREADY = "Connection already in progress",
            .EBADF = "Bad file number. There are two possible causes: 1) The specified file descriptor isn't a valid value or doesn't refer to an open file. 2) An attempt was made to write to a file or device opened for read-only access",
            .EBADMSG = "Bad message",
            .EBUSY = "Device or resource busy",
            .ECANCELED = "Operation canceled",
            .ECHILD = "No spawned processes",
            .ECONNABORTED = "Connection aborted",
            .ECONNREFUSED = "Connection refused",
            .ECONNRESET = "Connection reset",
            .EDEADLK = "Resource deadlock would occur",
            .EDEADLOCK = "Same as EDEADLK for compatibility with older Microsoft C versions",
            .EDESTADDRREQ = "Destination address required",
            .EDOM = "Math argument. The argument to a math function isn't in the domain of the function",
            .EEXIST = "Files exists. An attempt has been made to create a file that already exists. For example, the _O_CREAT and _O_EXCL flags are specified in an _open call, but the named file already exists",
            .EFAULT = "Bad address",
            .EFBIG = "File too large",
            .EHOSTUNREACH = "Host unreachable",
            .EIDRM = "Identifier removed",
            .EILSEQ = "Illegal sequence of bytes (for example, in an MBCS string).",
            .EINPROGRESS = "Operation in progress",
            .EINTR = "Interrupted function",
            .EINVAL = "Invalid argument. An invalid value was given for one of the arguments to a function. For example, the value given for the origin when positioning a file pointer (by a call to fseek) is before the beginning of the file",
            .EIO = "I/O error",
            .EISCONN = "Already connected",
            .EISDIR = "Is a directory",
            .ELOOP = "Too many symbolic link levels",
            .EMFILE = "Too many open files. No more file descriptors are available, so no more files can be opened",
            .EMLINK = "Too many links",
            .EMSGSIZE = "Message size",
            .ENAMETOOLONG = "Filename too long",
            .ENETDOWN = "Network down",
            .ENETRESET = "Network reset",
            .ENETUNREACH = "Network unreachable",
            .ENFILE = "Too many files open in system",
            .ENOBUFS = "No buffer space",
            .ENODATA = "No message available",
            .ENODEV = "No such device",
            .ENOENT = "No such file or directory. The specified file or directory doesn't exist or can't be found. This message can occur whenever a specified file doesn't exist or a component of a path doesn't specify an existing directory",
            .ENOEXEC = "Exec format error. An attempt was made to execute a file that isn't executable or that has an invalid executable-file format",
            .ENOLCK = "No locks available",
            .ENOLINK = "No link",
            .ENOMEM = "Not enough memory is available for the attempted operator. For example, this message can occur when insufficient memory is available to execute a child process, or when the allocation request in a _getcwd call can't be satisfied",
            .ENOMSG = "No message",
            .ENOPROTOOPT = "No protocol option",
            .ENOSPC = "No space left on device. No more space for writing is available on the device (for example, when the disk is full).",
            .ENOSR = "No stream resources",
            .ENOSTR = "Not a stream",
            .ENOSYS = "Function not supported",
            .ENOTCONN = "Not connected",
            .ENOTDIR = "Not a directory",
            .ENOTEMPTY = "Directory not empty",
            .ENOTRECOVERABLE = "State not recoverable",
            .ENOTSOCK = "Not a socket",
            .ENOTSUP = "Not supported",
            .ENOTTY = "Inappropriate I/O control operation",
            .ENXIO = "No such device or address",
            .EOPNOTSUPP = "Operation not supported",
            .EOTHER = "Other",
            .EOVERFLOW = "Value too large",
            .EOWNERDEAD = "Owner dead",
            .EPERM = "Operation not permitted",
            .EPIPE = "Broken pipe",
            .EPROTO = "Protocol error",
            .EPROTONOSUPPORT = "Protocol not supported",
            .EPROTOTYPE = "Wrong protocol type",
            .ERANGE = "Result too large. An argument to a math function is too large, resulting in partial or total loss of significance in the result. This error can also occur in other functions when an argument is larger than expected (for example, when the buffer argument to _getcwd is longer than expected).",
            .EROFS = "Read only file system",
            .ESPIPE = "Invalid seek",
            .ESRCH = "No such process",
            .ETIME = "Stream timeout",
            .ETIMEDOUT = "Timed out",
            .ETXTBSY = "Text file busy",
            .EWOULDBLOCK = "Operation would block",
            .EXDEV = "Cross-device link. An attempt was made to move a file to a different device (using the rename function",
            .STRUNCATE = "A string copy or concatenation resulted in a truncated string. See _TRUNCATE",
        });

        break :brk labels_;
    };
    comptime {
        @setEvalBranchQuota(9999999); <=====
    }
};

test {
    _ = SystemErrno.labels;
}
1 Like
10

Oh, I see! It’s truly a bug.