Question

If I would like to support the retrieval of few types from a database query in C++ I could create a method definition based on templates like

template<typename T>
T getDBValue(int col){
    throw "not implemented";
}

template<>
int getDBValue<int>(int col){
    return 43;
}

template<>
char* getDBValue<char*>(int col){
    return "foo";
}

I know that there is no real counterpart of templates in objective-c, so what what would you use to support few return values rather than implementing this like

- (type1) getType1FromCol: (int) col;
- (type2) getType2FromCol: (int) col;
- (type3) getType3FromCol: (int) col;

Thanks in advance!

Answer 1

You can always use Objective-C++ if you want to mix the languages, or if you find one is better suited for a particular task. Typically, you would compile as ObjC++ by changing the file extension to .mm.

For an ObjC interface, you could consider a simple wrapper interface like this, which uses your existing program:

template<typename T>
T getDBValue(int col); // << not defined

template<>
int getDBValue<int>(int col){
    return 43;
}

template<>
const char* getDBValue<const char*>(int col){
    return "foo";
}

You could approach it like this:

@implementation MONDBEntry
{
    int col;
}
...

- (int)intValue
{
    return getDBValue<int>(self.col);
}

- (NSString *)stringValue
{
    return [NSString stringWithUTF8String:getDBValue<const char*>(self.col)];
}
...