util::array

[Dave]

After a discussion with Ayin, we've decided to add a directive to the coding standards (http://wesnoth.slack.it/?CodingStandards) not to use C-style arrays in Wesnoth.

A wrapper to C-style arrays has been added in array.hpp, util::array. It should be used instead of C-style arrays at all times.

E.g.

Code: Select all

util::array<int,10> myints;

instead of,

Code: Select all

int myints[10];

David

[mlangsdorf]

What's the rational behind this? I'm not questioning the decision, I just don't have any idea why it was made.

[Dave]

What's the rational behind this? I'm not questioning the decision, I just don't have any idea why it was made.

Because C-style arrays are ugly to use, and the interface is inconsistent with C++-style container classes.

E.g. to iterate over an array of integers:

Code: Select all

for(int* i = myarray; i != myarray + sizeof(myarray)/sizeof(*myarray); ++i) {
    ...
}

Which is very different from the vector way:

Code: Select all

for(vector<int>::iterator i = myarray.begin(); i != myarray.end(); ++i) {
    ...
}

The new way to do it with an array is consistent with this:

Code: Select all

for(array<int,n>::iterator i = myarray.begin(); i != myarray.end(); ++i) {
    ...
}

(Note that if anyone wants to say that either way is hideously ugly, I won't disagree with them.)

David

[torangan]

What's the reasoning behind adding an own wrapper? It's not as if std::vector<> would be more then a quite sophisticated wrapper. I doubt that you can implement any of the wrapper functions more efficient then std::vector<> because as part of the c++ library, it'll most likely use compiler specific optimizations normal user won't ever know of.

[Dave]

What's the reasoning behind adding an own wrapper? It's not as if std::vector<> would be more then a quite sophisticated wrapper. I doubt that you can implement any of the wrapper functions more efficient then std::vector<> because as part of the c++ library, it'll most likely use compiler specific optimizations normal user won't ever know of.

std::vector is less efficient because it allocates memory dynamically (on the free store), while a C-style array allocates it on the stack, which is extremely fast.

The util::array I added is a very very thin wrapper over a C-style array. It's similiar to the wrapper in Boost. I just wrote my own because it was about as simple to write it myself as it was to extract the code from Boost while getting rid of the Boost header dependencies and weird code to handle strange compilers.

David

[torangan]

Well sure, I just didn't think about small, stack allocated arrays. You should have written that it's intended to be used for stack allocated arrays and std::vector for heap allocated arrays. Or I should have thought a moment longer, either would've done it.

[Dave]

Well sure, I just didn't think about small, stack allocated arrays. You should have written that it's intended to be used for stack allocated arrays and std::vector for heap allocated arrays. Or I should have thought a moment longer, either would've done it.

Huh? My entire first post in this thread said exactly that.

David

[torangan]

Yes, if read correctly it does say it. I got set of by "at all times" and got the picture of int[] foo = new int[...] into my mind which should be replaced by vector instead of another wrapper IMHO.

[Dave]

got the picture of int[] foo = new int[...] into my mind

Sounds like you've been programming too much Java or C#

David

[torangan]

Well it's legal syntax in C++ as well, but yes, I've been forced to program in Java for more then a year now. I do like C++ way more but the decision is made by those who pay the money I want. When I'm coding open source, it's always C++ though.

[Dave]

Well it's legal syntax in C++ as well, but yes, I've been forced to program in Java for more then a year now. I do like C++ way more but the decision is made by those who pay the money I want. When I'm coding open source, it's always C++ though.

It's not legal syntax in C++. In C++ you go,

int* foo = new int[...];

or you can go,

int foo[] = {...};

but never int[] foo

David