Function directEnumArrayLen [src]

Determines the length of a direct-mapped enum array, indexed by @intCast(usize, @intFromEnum(enum_value)). If the enum is non-exhaustive, the resulting length will only be enough to hold all explicit fields. If the enum contains any fields with values that cannot be represented by usize, a compile error is issued. The max_unused_slots parameter limits the total number of items which have no matching enum key (holes in the enum numbering). So for example, if an enum has values 1, 2, 5, and 6, max_unused_slots must be at least 3, to allow unused slots 0, 3, and 4.

Prototype

pub fn directEnumArrayLen(comptime E: type, comptime max_unused_slots: comptime_int) comptime_int

Parameters

E: typemax_unused_slots: comptime_int

Source

  pub fn directEnumArrayLen(comptime E: type, comptime max_unused_slots: comptime_int) comptime_int {
    var max_value: comptime_int = -1;
    const max_usize: comptime_int = ~@as(usize, 0);
    const fields = @typeInfo(E).@"enum".fields;
    for (fields) |f| {
        if (f.value < 0) {
            @compileError("Cannot create a direct enum array for " ++ @typeName(E) ++ ", field ." ++ f.name ++ " has a negative value.");
        }
        if (f.value > max_value) {
            if (f.value > max_usize) {
                @compileError("Cannot create a direct enum array for " ++ @typeName(E) ++ ", field ." ++ f.name ++ " is larger than the max value of usize.");
            }
            max_value = f.value;
        }
    }

    const unused_slots = max_value + 1 - fields.len;
    if (unused_slots > max_unused_slots) {
        const unused_str = std.fmt.comptimePrint("{d}", .{unused_slots});
        const allowed_str = std.fmt.comptimePrint("{d}", .{max_unused_slots});
        @compileError("Cannot create a direct enum array for " ++ @typeName(E) ++ ". It would have " ++ unused_str ++ " unused slots, but only " ++ allowed_str ++ " are allowed.");
    }

    return max_value + 1;
}  