How to idiomatically call C ++ functions based on a variable value?

Question

Suppose I have a data type enum TreeTypes { TallTree, ShortTree, MediumTree }.

And I have to initialize some data based on one specific type of tree.

I have currently written this code:

int initialize(enum TreeTypes tree_type) {
    if (tree_type == TallTree) {
        init_tall_tree();
    }
    else if (tree_type == ShortTree) {
        init_short_tree();
    }
    else if (tree_type == MediumTree) {
        init_medium_tree();
    }
    return OK;
}

But this is some kind of silly code repetition. I do not use any of the powerful C ++ features such as templates.

How can I write this code better?

Thanks, Boda Sido.

Answer 1

Your code is fine for two or three values, but you're right, you need something more industrial when you have hundreds of them. Two possible solutions:

• , - ,

• enum → , - - map[enum]->func()

, , .

Answer 2

:

class Tree { public: virtual void initialize() = 0; }

class ShortTree : public Tree {
public:
    virtual void initialize(){
        /* Short Tree specific code here */
    }
}

class MediumTree : public Tree {
public:
    virtual void initialize(){
        /* Medium Tree specific code here */
    }
}

class TallTree : public Tree {
public:
    virtual void initialize(){
        /* Tall Tree specific code here */
    }
}

, , , :

Vector<Tree*> trees;
trees.push_back(new SmallTree());
trees.push_back(new MediumTree();
trees.push_back(new TallTree();

// This will call the tree specific code for each tree in the vector
for(vector<Tree*>::iterator tree = trees.begin(); tree!=trees.end(); ++tree)
    tree->initialize();

Answer 3

, ( , ), :

enum TreeTypes { TallTree, ShortTree, MediumTree, MaxTreeTypes }

typedef void (*p_init_func)(void); 

p_init_func initialize_funcs[MaxTreeTypes] =
{
    &init_tall_tree, 
    &init_short_tree,
    &init_medium_tree
};

int initialize(enum TreeTypes tree_type)
{ 
    initialize_funcs[tree_type]();
    return OK; 
} 

Answer 4

switch:

int initialize(enum TreeTypes tree_type) {
    switch (tree_type) {
        case TallTree: 
            init_tall_tree();
            break;
        case ShortTree:
            init_short_tree();
            break;
        case MediumTree:
            init_medium_tree();
            break;
    }
    return OK;
}

Answer 5

, , .

... , , if/else -.

, , , , .

Answer 6

, :

enum TreeTypes { Tall, Short, Medium };

struct TreeBase {
    // (...)
};

struct TallTree : public TreeBase {
    // (...)
};

struct ShortTree : public TreeBase {
    // (...)
};

struct MediumTree : public TreeBase {
    // (...)
};

template<TreeTypes N_type = Tall>
struct Tree : public TallTree {
    // (...)
};

template<>
struct Tree<Short> : public ShortTree {
    // (...)
};

template<>
struct Tree<Medium> : public MediumTree {
    // (...)
};

, , . :

Tree<Tall> tall_tree;
Tree<Short> short_tree;
Tree<Medium> medium_tree;