weak_type_checking.c

#include <stdio.h>
#include <stdlib.h>


// Type Definitions

// These are the type definitions that can be used to check for type
// They need to be unique so that only types starting with these
// prefixes will be presumed to be of the type specified.
typedef enum type {
    TYPE_StateRequester = 0x10f3ccd3,
    TYPE_OtherThing = 0x09331c8c
} type;


// State Requester Definitions & Functions

typedef int state_requester_f(void* request_parameters);

// Since we want to check the "type" of a function reference,
// we need to wrap it in a struct along with it's type code.
struct state_requester_t {
    int type;
    state_requester_f* call;
} typedef state_requester_t;

state_requester_t new_state_requester(state_requester_f* call) {
    state_requester_t sr;
    sr.type = TYPE_StateRequester;
    sr.call = call;
    return sr;
}

// This function will check if data is of type StateRequester
// 
// If the data sent to this function is not of the length
// nessecary for the state_requester type, - OR - 
// it's type property is not equal to the StateRequester type
// then we will presume that this data is NOT of type StateRequester
uint8_t is_state_requester(void* data, size_t len) {
    return len == sizeof(state_requester_t) && 
           ((state_requester_t*)data)->type == TYPE_StateRequester;
}


// Testing functions

int test_caller(void* data) {
    printf("Got to the test_caller function.\n");

    return 0;
}

int main(int agc, char *argv[]) {

    // Create an actual state_requester_t definitiion
    state_requester_t sr = new_state_requester(&test_caller);

    // Test to see if it's validated as a state_requester_t
    if (is_state_requester(&sr, sizeof(state_requester_t))) {
        printf("Yes, variable 'sr' is presumadely of type state_requester_t\n");
        sr.call(NULL);
    } else {
        printf("No, variable 'sr' is not of type state_requester_t\n");
    }

    // Create a phony state_requester_t definition,
    // but keep it the same length as a regular
    // state_requester_t
    void* a = malloc(sizeof(state_requester_t));

    // Test to see if it's validated as a state_requester_t
    if (is_state_requester(a, sizeof(state_requester_t))) {
        printf("Yes, variable 'a' is presumadely of type state_requester_t\n");
    } else {
        printf("No, variable 'a' is not of type state_requester_t\n");
    }

    free(a);

    // Create a phony state_requester_t with an improper length
    void* b = malloc(5);

    // Test to see if it's validated as a state_requester_t 
    if (is_state_requester(b, sizeof(state_requester_t))) {
        printf("Yes, variable 'b' is presumadely of type state_requester_t\n");
    } else {
        printf("No, variable 'b' is not of type state_requester_t\n");
    }    

    free(b);

    return 0;
}