How would you define a simple “min” method in obj-c

Question

I want to define a min and max methods in a Utils class.

@interface Utils

int min(int a, int b);
int max(int a, int b);

@end

But I don\'t

Answer 1

There's a serious issue with the solution posted by Brandon Bodnár (which by the time of this writing is marked as a valid solution).

Issue described here: http://gcc.gnu.org/onlinedocs/gcc-3.4.6/gcc/Min-and-Max.html And the (valid & secure) solution to it: http://gcc.gnu.org/onlinedocs/gcc-3.4.6/gcc/Typeof.html

Check it out yourself:

#include 

#define NAIVE_MAX(a,b) (a > b ? a : b)

#define NAIVE_MIN(a,b) (a < b ? a : b)

#if !defined MAX
#define MAX(a,b) \
({ __typeof__ (a) __a = (a); \
__typeof__ (b) __b = (b); \
__a > __b ? __a : __b; })
#endif

#if !defined MIN
#define MIN(a,b) \
({ __typeof__ (a) __a = (a); \
__typeof__ (b) __b = (b); \
__a < __b ? __a : __b; })
#endif

int main (int argc, const char * argv[]) {
    int a = 3;
    int b = 5;

#pragma mark NON-FATAL CASES:
    printf("NAIVE_MAX(%d, %d) => %d\n", a, b, NAIVE_MAX(a, b));
    printf("NAIVE_MIN(%d, %d) => %d\n", a, b, NAIVE_MIN(a, b));

    printf("MAX(%d, %d) => %d\n", a, b, MAX(a, b));
    printf("MIN(%d, %d) => %d\n", a, b, MIN(a, b));

    printf("\nEverything fine so far...\n\n");

#pragma mark FATAL CASES:
    //cache:
    int _a = a;
    int _b = b;
    printf("NAIVE_MAX(%d++, %d++) => %d\n", _a, _b, NAIVE_MAX(a++, b++));

    //reset:
    a = _a;
    b = _b;
    printf("NAIVE_MIN(%d++, %d++) => %d\n", _a, _b, NAIVE_MIN(a++, b++));

    //reset:
    a = _a;
    b = _b;
    printf("NAIVE_MAX(++%d, ++%d) => %d\n", _a, _b, NAIVE_MAX(++a, ++b));

    //reset:
    a = _a;
    b = _b;
    printf("NAIVE_MIN(++%d, ++%d) => %d\n", _a, _b, NAIVE_MIN(++a, ++b));

    printf("\nOuch, this doesn't look right at all!\n\n");

#pragma mark NON-FATAL CASES:
    //reset:
    a = _a;
    b = _b;
    printf("MAX(%d++, %d++) => %d\n", _a, _b, MAX(a++, b++));

    //reset:
    a = _a;
    b = _b;
    printf("MIN(%d++, %d++) => %d\n", _a, _b, MIN(a++, b++));

    //reset:
    a = _a;
    b = _b;
    printf("MAX(++%d, ++%d) => %d\n", _a, _b, MAX(++a, ++b));

    //reset:
    a = _a;
    b = _b;
    printf("MIN(++%d, ++%d) => %d\n", _a, _b, MIN(++a, ++b));

    printf("\nAh, much better now.\n\n");

    return 0;
}

Console log:

NAIVE_MAX(3, 5) => 5
NAIVE_MIN(3, 5) => 3
MAX(3, 5) => 5
MIN(3, 5) => 3

Everything fine so far...

NAIVE_MAX(3++, 5++) => 6
NAIVE_MIN(3++, 5++) => 4
NAIVE_MAX(++3, ++5) => 7
NAIVE_MIN(++3, ++5) => 5

Ouch, this doesn't look right at all!

MAX(3++, 5++) => 5
MIN(3++, 5++) => 3
MAX(++3, ++5) => 6
MIN(++3, ++5) => 4

Ah, much better now.

So never ever use the naive implementation as seen in the code above (and as suggested by Brandon Bodnár, sorry buddy ;) ) if you want to avoid worst cases like these.