What is a better way to check if string is a member of a const struct?

Question

I want to check if a string is in a const struct. The way I do it is like this:

In my MyClass.h:

extern const struct MyAttributes {
    __unsafe_unretained NSString *attribute1;
    __unsafe_unretained NSString *attribute2;
    __unsafe_unretained NSString *attribute3;
    __unsafe_unretained NSString *attribute4;
    __unsafe_unretained NSString *attribute5;
} MyAttributes;

Then in my MyClass.m I have:

const struct MyAttributes MyAttributes = {
    .attribute1 = @"attribute1",
    .attribute2 = @"attribute2",
    .attribute3 = @"attribute3",
    .attribute4 = @"attribute4",
    .attribute5 = @"attribute5"
};

...

- (void)someMethod
{
    BOOL test1 = [self check:@"test"];
    BOOL test2 = [self check:@"attribute1"];
}

- (BOOL)check:(NSString *)string
{
    return [string isEqualToString:MyAttributes.attribute1] ||
        [string isEqualToString:MyAttributes.attribute2] ||
        [string isEqualToString:MyAttributes.attribute3] ||
        [string isEqualToString:MyAttributes.attribute4] ||
        [string isEqualToString:MyAttributes.attribute5];
}

Well, this works. But, is there a better way to implement - (void)check so that, if I update MyAttributes, I won't have to update - (void)check?

You don't have to use `-isEqualToString:`, `-isEqual:` works just fine. — Christian Schnorr, Sep 26 '13 at 11:38
@Jenox Since they both work, what should be the pro of using isEqual:? — Ramy Al Zuhouri, Sep 26 '13 at 11:39
It's less code, so your lines are shorter and easier to read ;) — Christian Schnorr, Sep 26 '13 at 11:40
@Jenox, yes you're right. But, what I really wanted is to implement -check: once that if I add or remove something from MyAttributes I won't have to touch this method again. — yoninja, Sep 26 '13 at 11:49
Why do you need to use a struct for this? Just have the array as some sort of global, a separate enum for the indexes (if you wish) and use array membership for your check. — Hot Licks, Sep 26 '13 at 12:11

Ramy Al Zuhouri · Accepted Answer · 2013-09-26T12:06:49.380

You can convert it to an Objective-C array and then see if it contains the string you're looking for:

- (BOOL) check: (NSString*) string {
    // I renamed the variable MyAttributes to myAttributes, following naming conventions
    __unsafe_unretained id* ptr;
    struct MyAttributes* attrPtr= &myAttributes;
    memcpy(&ptr, &attrPtr, sizeof(id*));
    NSArray* array= [NSArray arrayWithObjects: ptr count: sizeof(MyAttributes)/sizeof(NSString*)];
    return [array containsObject: string];
}

The C-style way is to treat the struct as a C-array:

- (BOOL)check:(NSString *)string {
    BOOL result= NO;
    // I renamed the variable MyAttributes to myAttributes, following naming conventions
    NSString* __unsafe_unretained * strPtr;
    struct MyAttributes* ptr= &myAttributes;
    memcpy(&strPtr, &ptr, sizeof(NSString**));
    for(size_t i=0; i<sizeof(MyAttributes)/sizeof(NSString*) && !result;i++) {
        result= [string isEqualToString: strPtr[i] ];
    }
    return result;
}

PS: I used memcpy to avoid bridge-casting, since the strings are already retained in myAttributes.

score 0 · Answer 2 · edited Jun 20 '20 at 09:12

0

you can dig in the direction of keeping struct items in NSArray

Possible answer:

Cocoa structs and NSMutableArray

then in - check method use containsObject: or array iteration to check if string is there.

edited Jun 20 '20 at 09:12

Community

1
1

answered Sep 26 '13 at 10:52

Injectios

2,777
1
30
50

- (BOOL)containsObject:(id)anObject Description Returns a Boolean value that indicates whether a given object is present in the array. This method determines whether anObject is present in the array by sending an isEqual: message to each of the array’s objects (and passing anObject as the parameter to each isEqual: message). – Voda Ion Sep 26 '13 at 11:20
well... yes.. the main idea was: converting to array – Injectios Sep 26 '13 at 11:22
I guess this solution actually stores the struct as one object into the array. What could be the way to store the contents of the struct as individual objects to an array? – yoninja Sep 26 '13 at 11:53
http://stackoverflow.com/questions/6212815/how-can-i-create-an-nsmutablearray-of-structs – Injectios Sep 26 '13 at 11:56

What is a better way to check if string is a member of a const struct?

2 Answers2