typedef function pointer array declaration problem Thanks for all your feedback. It helped.

I rewrote this yet another time and this time it works perfectly. I included three variations: a simple example using an array of function pointers, a Lambda version and a complex version like what I started with.

#define TASK_COUNT          3

typedef void ( *taskPointer ) ( );

//  Simple Version:
void taskS1 () { Serial.println ( ( char* )"SIMPLE TASK 1" ); }
void taskS2 () { Serial.println ( ( char* )"SIMPLE TASK 2" ); }
void taskS3 () { Serial.println ( ( char* )"SIMPLE TASK 3" ); }

//  Array of pointers to tasks
taskPointer callSimpleTask [ ] = {
taskS1,
taskS2,
taskS3,
};

//  Run the simple test
void showSimpleVersion () {
    Serial.println ( F ( "\nSimple Version:" ) );
    for (uint8_t i = 0; i &lt; TASK_COUNT; i++) {
        callSimpleTask [ i ] ();
    }

}

//  Lambda Version: No separate task definitoins
void ( *callLambdaTask [ ] ) ( ) = {
    [ ] {Serial.println ( ( char* )"LAMBDA TASK 1" ); },
    [ ] {Serial.println ( ( char* )"LAMBDA TASK 2" ); },
    [ ] {Serial.println ( ( char* )"LAMBDA TASK 3" ); },
};

//  Run the Lambda test
void showLambdaVersion () {
    Serial.println ( F ( "\nLambda Version:" ) );
    for (uint8_t i = 0; i &lt; TASK_COUNT; i++) {
        callLambdaTask [ i ] ();
    }

}

//  Complex Version: Each array element is a struct containing a 
//  pointer to the corresponding task and related properties
struct complexTaskDefinition {
    taskPointer task;
    bool repeat;                //  Repeat flashing after delay
    int32_t iterations;         //  # times to repeat... -1 = forever
    uint32_t delay;             //  MS to wait before execution
};

//  Create a pointer to a task definition
complexTaskDefinition *task;

//  Prove that called function can call other functions:
void taskC1 () { showTaskC1(); }
void taskC2 () { showTaskC1 (); }
void taskC3 () { showTaskC1 (); }

void showTaskC1 () {
    Serial.println ( ( char* )"COMPLEX TASK 1" );
}
void showTaskC2 () {
    Serial.println ( ( char* )"COMPLEX TASK 2" );
}
void showTaskC3 () {
    Serial.println ( ( char* )"COMPLEX TASK 3" );
}

complexTaskDefinition tasks [ ] [4] = {
    {taskC1, true, -1, 1000 },  //  taskC1 repeats forever every second
    {taskC2, true, 10, 2000 },  //  taskC2 runs 10 times pausing for 2 seconds between iterations
    {taskC3, false, 3, 3000 },  //  taskC3 runs 3 times with 3 second delays between each, then dies
};

void showComplexTaskList () {
    Serial.println ( F ( "\nComplex Task List:" ) );
    for (uint8_t i = 0; i &lt; TASK_COUNT; i++) {
        task = tasks [ i ];
        Serial.print ( '[' );
        Serial.print ( i );
        Serial.print ( F ( "] REPEAT:" ));
        Serial.print ( ( task-&gt;repeat ) ? "YES" : "NO" );
        Serial.print ( F ( ", DELAY:" ) );
        Serial.print ( task-&gt;delay );
        Serial.print ( F ( ", ITERATIONS:" ) );
        Serial.print ( task-&gt;iterations );
        Serial.println ();
    }
}

void showComplexVersion () {
    Serial.println ( F ( "\nComplex Version:" ) );
    for (uint8_t i = 0; i &lt; TASK_COUNT; i++) {
        task = tasks [ i ];
        task-&gt;task ();
//      (( *tasks ) [ i ]).task ();
    }
}

void setup () {
    Serial.begin ( 115200 );
    while (!Serial.availableForWrite ()) {}

    showSimpleVersion ();

    showLambdaVersion ();

    showComplexVersion ();

    showComplexTaskList ();
}

void loop () {
}


Here is the output:
Simple Version:

SIMPLE TASK 1
SIMPLE TASK 2
SIMPLE TASK 3

Lambda Version:
LAMBDA TASK 1
LAMBDA TASK 2
LAMBDA TASK 3

Complex Version:
COMPLEX TASK 1
COMPLEX TASK 1
COMPLEX TASK 1

Complex Task List:
[0] REPEAT:YES, DELAY:1000, ITERATIONS:-1
[1] REPEAT:YES, DELAY:2000, ITERATIONS:10
[2] REPEAT:NO, DELAY:3000, ITERATIONS:3


I want to run one more experiment, this time with the complex version as a class.
Try replacing

taskDefinition _tasks [ ] [4] = {


by

taskDefinition _tasks [ ] = {


In short, you have defined _tasks as a 2D array of objects (an array
of arrays of objects) while you intend to use it as a 1D array.



Note that the error message is quite explicit if you take the time to
parse it:


  request for member 'task' in '_tasks[((int)i)]',


You are requesting _tasks[i].task,


  which is of non-class type


but _tasks[i] is not an object.


  type 'taskDefinition [4]'


It is instead an array of four taskDefinition objects.



Edit: Fixing the answer to match the latest version of the question.

Your code works, but not quite as you expect it to work. You wrote:

complexTaskDefinition tasks [ ] [4] = ...;


Here you are defining a 2D array of objects, while your intention was to
define a one-dimensional array (why do I feel like I am repeating
myself?).

complexTaskDefinition tasks [ ] [4] = {
    {taskC1, true, -1, 1000 },
    {taskC2, true, 10, 2000 },
    {taskC3, false, 3, 3000 },
};


This definition, although syntactically correct, is awfully wacky. You
are defining tasks as an array of 3 items. Each item is itself an
array of 4 objects, where the first object of the array is explicitly
initialized, and the three others are implicitly initialized to
all-bits-zero. So basically your definition is equivalent to this
explicit version:

complexTaskDefinition tasks [3] [4] = {
    {{taskC1, true, -1, 1000 }, {nullptr, false, 0, 0},
     {nullptr, false, 0, 0},    {nullptr, false, 0, 0}},
    {{taskC2, true, 10, 2000 }, {nullptr, false, 0, 0},
     {nullptr, false, 0, 0},    {nullptr, false, 0, 0}},
    {{taskC3, false, 3, 3000 }, {nullptr, false, 0, 0},
     {nullptr, false, 0, 0},    {nullptr, false, 0, 0}}
};


Then you wrote:

task = tasks [ i ];


Here, tasks[i] is a row of the 2D array, i.e. a 1D array of 4 objects,
whereas task is a pointer to object. The assignment is legit because
here, like in most contexts, the array “decays” to a pointer to its
first element. The above line is equivalent to the explicit version:

task = &amp;tasks[i][0];


Quite fortunately, this happens to point to one of the elements of the
array that has been explicitly initialized!

As an illustration of the above, here is a modified version of
showComplexTaskList() that loops over all the tasks in the array:

void showComplexTaskList () {
    Serial.println ( F ( "\nComplex Task List:" ) );
    Serial.print(F("number of tasks: "));
    Serial.println(sizeof tasks / sizeof(complexTaskDefinition));
    for (uint8_t i = 0; i &lt; TASK_COUNT; i++) {
        for (uint8_t j = 0; j &lt; 4; j++) {
            task = &amp;tasks[i][j];
            Serial.print ( '[' );
            Serial.print ( i );
            Serial.print ( F ("]["));
            Serial.print ( j );
            Serial.print ( F ( "] REPEAT:" ));
            Serial.print ( ( task-&gt;repeat ) ? "YES" : "NO" );
            Serial.print ( F ( ", DELAY:" ) );
            Serial.print ( task-&gt;delay );
            Serial.print ( F ( ", ITERATIONS:" ) );
            Serial.print ( task-&gt;iterations );
            Serial.println ();
        }
    }
}


Its output is:

Complex Task List:
number of tasks: 12
[0][0] REPEAT:YES, DELAY:1000, ITERATIONS:-1
[0][1] REPEAT:NO, DELAY:0, ITERATIONS:0
[0][2] REPEAT:NO, DELAY:0, ITERATIONS:0
[0][3] REPEAT:NO, DELAY:0, ITERATIONS:0
[1][0] REPEAT:YES, DELAY:2000, ITERATIONS:10
[1][1] REPEAT:NO, DELAY:0, ITERATIONS:0
[1][2] REPEAT:NO, DELAY:0, ITERATIONS:0
[1][3] REPEAT:NO, DELAY:0, ITERATIONS:0
[2][0] REPEAT:NO, DELAY:3000, ITERATIONS:3
[2][1] REPEAT:NO, DELAY:0, ITERATIONS:0
[2][2] REPEAT:NO, DELAY:0, ITERATIONS:0
[2][3] REPEAT:NO, DELAY:0, ITERATIONS:0


So your program works almost by chance: an error in the way you define
the array cancels an error in the way you use it. This kind of cancelled
error method is very bad programming practice. You are wasting memory in
unused complexTaskDefinition objects. More importantly, your code
doesn't express your intent, which makes the program way harder to
understand and to debug.

The fix is to declare a 1D array, as this has always been the intention:

complexTaskDefinition tasks [ ] = {
    {taskC1, true, -1, 1000 },
    {taskC2, true, 10, 2000 },
    {taskC3, false, 3, 3000 },
};


Now, you can check that this array does only have three tasks, as
reported by sizeof tasks / sizeof(complexTaskDefinition). To use the
array, you can use a pointer if you want:

task = &amp;tasks[i];
// ...
Serial.print ( ( task-&gt;repeat ) ? "YES" : "NO" );


Or you can directly request a member of tasks[i], as in

void showComplexVersion () {
    Serial.println ( F ( "\nComplex Version:" ) );
    for (uint8_t i = 0; i &lt; TASK_COUNT; i++) {
        tasks[i].task();
    }
}


Now I have a question for you. Since I already explained your 1D vs. 2D
array mistake in the first iteration of my answer, why did you persist
with this in your edited question? If you are going to blatantly ignore
the answers you get, at least say so in the question. This could save
time to those who might consider helping you.