使用协议的程序示例（193）

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最新推荐文章于 2022-05-30 15:06:50 发布

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分类专栏： Objective-C 读书笔记

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本文介绍了一个使用 Objective-C 实现的数值类扩展方案，包括分数类 Fraction 的定义与实现，以及对 NSArray 和 NSString 类的功能增强。实现了分数的加减乘除运算，并通过遵守 RealNumber 协议确保所有数值类型可以统一比较大小。

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@protocol RealNumber
- (double)realValue;
@end

#import <Foundation/NSArray.h>
#import "RealNumber.h"

@interface NSMutableArray (RealArray)
- (void)addRealNumber:(id <RealNumber>)number;
- (void)sort;
@end

#import "RealArray.h"

@implementation NSMutableArray (RealArray)

- (void)addRealNumber:(id <RealNumber>)number {
    [self addObject:number];
}

static NSInteger compareReal(id <RealNumber>a, id <RealNumber>b, void *_) {
    double v = [a realValue] - [b realValue];
    if (v > 0.0) return NSOrderedDescending;
    if (v < 0.0) return NSOrderedAscending;
    return NSOrderedSame;
}

- (void)sort {
    [self sortUsingFunction:compareReal context:0];
}

@end

#import <Foundation/NSObject.h>
#import "RealNumber.h"

@class NSString;

@interface Fraction : NSObject <RealNumber>
{
    int sgn;   // sign
    int num;   // numerator
    int den;   // denominator
}

+ (id)fractionWithNumerator:(int)n denominator:(int)d;
- (id)initWithNumerator:(int)n denominator:(int)d;
- (Fraction *)add:(Fraction *)obj;
- (Fraction *)sub:(Fraction *)obj;
- (Fraction *)mul:(Fraction *)obj;
- (Fraction *)div:(Fraction *)obj;
- (NSString *)description;

@end

#import "Fraction.h"
#import <Foundation/NSString.h>
#import <stdlib.h>
#import <float.h>

@implementation Fraction

static int gcd(int a, int b) // Greatest Common Divisor
{
    if (a < b)
        return gcd(b, a);
    if (b == 0)
        return a;
    return gcd(b, a % b);
}

/* Local Method */
- (void)reduce
{
    int d;
    
    if (num == 0) {
        sgn = 1;
        den = 1;
        return;
    }
    if (den == 0) { // infinity
        num = 1;
        return;
    }
    if ((d = gcd(num, den)) == 1)
        return;
    num /= d;
    den /= d;
}

/* make a temporary instance */
+ (id)fractionWithNumerator:(int)n denominator:(int)d
{
    return [[self alloc] initWithNumerator:n denominator:d] ;
}

#define  SIGN(a)    ( ((a) >= 0) ? 1 : (-1) )

/* Designated Initializer */
- (id)initWithNumerator:(int)n denominator:(int)d
{
    if ((self = [super init]) != nil) {
        sgn = SIGN(n) * SIGN(d);
        num = abs(n);
        den = abs(d);
        [self reduce];
    }
    return self;
}

- (Fraction *)add:(Fraction *)obj
{
    int n, d;
    
    if (den == obj->den) {
        n = sgn * num + obj->sgn * obj->num;
        d = den;
    }else {
        n = sgn * num * obj->den + obj->sgn * obj->num * den;
        d = den * obj->den;
    }
    return [Fraction fractionWithNumerator:n denominator:d];
}

- (Fraction *)sub:(Fraction *)obj
{
    Fraction *tmp;
    tmp = [Fraction fractionWithNumerator: -1 * obj->sgn * obj->num
                              denominator: obj->den];
    return [self add: tmp];
}

- (Fraction *)mul:(Fraction *)obj
{
    int n = sgn * obj->sgn * num * obj->num;
    int d = den * obj->den;
    return [Fraction fractionWithNumerator:n denominator:d];
}

- (Fraction *)div:(Fraction *)obj
{
    int n = sgn * obj->sgn * num * obj->den;
    int d = den * obj->num;
    return [Fraction fractionWithNumerator:n denominator:d];
}

- (NSString *)description
{
    int n = (sgn >= 0) ? num : -num;
    return (den == 1)
    ? [NSString stringWithFormat:@"%d", n]
    : [NSString stringWithFormat:@"%d/%d", n, den];
}

/*protocol implemented*/
- (double)realValue {
    if (den == 0) return DBL_MAX;
    return (double)(sgn * num) / (double)den;
}

@end

#import <Foundation/NSString.h>
#import "RealNumber.h"

@interface NSString (Real) <RealNumber>
@end

#import "NSStringReal.h"

@implementation NSString (Real)

- (double)realValue {
    return [self doubleValue];
}

@end

#import <Foundation/Foundation.h>
#import <stdio.h>
#import "RealNumber.h"
#import "Fraction.h"
#import "NSStringReal.h"
#import "RealArray.h"

int main(void) {
    @autoreleasepool {
        id array = [NSMutableArray array];
        [array addRealNumber:@"1.3"];
        [array addRealNumber:@"0.35"];
        [array addRealNumber:@"0.2"];
        [array addRealNumber:[Fraction fractionWithNumerator:1 denominator:3] ];
        [array addRealNumber:[Fraction fractionWithNumerator:3 denominator:8] ];
        [array addRealNumber:[Fraction fractionWithNumerator:3 denominator:2] ];
        [array sort];
        printf("%s\n", [[array description] UTF8String]);
    }
    return 0;
}