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

问题:

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 want to have named parameters. It would be a too heavy notation. I wanted to use the C-style definition. But then [Utils min(a, b)] as a call doesn't work. What is my problem?

Thanks in advance for any help

回答1:

Since you aren't using the OS X Implementation of objective-c, you may not have access to the predefined MIN and MAX macros.

You can define these yourself as

#define MIN(a,b)    ((a) < (b) ? (a) : (b))
#define MAX(a,b)    ((a) > (b) ? (a) : (b))

There is probably a better way to define them, but these will create the simple macros for your use. You can add them into any common .h file that your classes normally share.

回答2:

It is already defined as a macro.

MIN(a, b)

MAX(a, b)

You dont need to redefine these ones.

回答3:

There's a serious security 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 <stdio.h>

#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.

回答4:

This is probably not a good idea for this particular application, but it is possible to write Objective-C methods with parameters “without names”, or rather with zero-length names:

+ min:(int)a :(int)b;
...
[Utils min:a :b]

(The selector would be @selector(min::).)

回答5:

Objective-C class methods use named parameters, period. That's just the way it is.

Why not make it a global, free function? You shouldn't need a Utils class for this kind of thing.

If you don't want to clutter the global namespace, you could use Objective-C++ (rename all .m files to .mm) and put it in a namespace.

回答6:

In a template file named "XXIntegerMath.h" drop this...

#import <Foundation/Foundation.h>

static inline NSInteger imax(NSInteger a, NSInteger b) {
    return  a > b ? a : b;
}

static inline NSInteger imin(NSInteger a, NSInteger b) {
    return  a < b ? a : b;
}

Then in your objective-c class ...

#import "XXIntegerMath.h"
NSInteger minValue = imin(someValue, someOtherValue);

It doesn't suffer from the problems described by Regexident.