Is it possible to write an in_array helper function using std library's find, begin and end?

Question

There is an answer on SO which explains how to perform a search for a value in an array. Coming from a PHP background, I am used to a degree of dynamic typization - something not present in C++, which then poses several challenges. Would it be then possible to create a helper function that would perform analogous to PHP's in_array($needle, $haystack) (for example, using the code from the linked answer) to be used as a shorthand?

Having written this snippet, I understand (tangibly) why it doesn't work - the parameters don't really have types signified. What, if anything, could be done to circumvent this, and would it be bad practice to do so?

bool in_array(needle, haystack) {
    // Check that type of needle matches type of array elements, then on check pass:
    pointer* = std::find(std::begin(haystack), std::end(haystack), needle);
    return pointer != std::end(haystack);
}

Edit: To be extra clear, I don't really want to PHPize C++ - what I was looking for is a way it's usually done in C++!

C++ is statically typed; You may want to use std::any to simulate PHP but the proper procedure is to get familiar with static types. — Michael Chourdakis
– Michael Chourdakis, Commented Jun 18, 2019 at 10:36
That's exactly what I'm trying to do, actually! Matter of fact, if there's a way to do this with static types, I would absolutely love that, because the only idea I have so far is just making an in_array function for each type I might need it for. — Ivan T.
– Ivan T., Commented Jun 18, 2019 at 10:38
In C++ we use templates to avoid rewriting a function for each type. — Michael Chourdakis
– Michael Chourdakis, Commented Jun 18, 2019 at 10:39
Trying to get one language to work like another is typically the first mistake, when learning a new one. C++ will not treat you well until you start leaning into its strengths. Forget about duck-typing, and start over. — sp2danny
– sp2danny, Commented Jun 18, 2019 at 10:43

Yksisarvinen · Accepted Answer · 2019-06-18 11:00:00Z

4

That's what templates are for:

template <class ValueType, class Container>
bool in_array(const ValueType& needle, const Container& haystack) {
// Check that type of needle matches type of array elements, then on check pass:
    return std::find(std::begin(haystack), std::end(haystack), needle) != std::end(haystack);
}

Provided that Container type is either a C-style array or it has accessible member methods begin() and end(); and that ValueType is convertible to Container::value_type, this should work.

This being said, templates are not an easy topic to handle. If you want to learn more, I recommend you one of good C++ books

edited Jun 18, 2019 at 11:00

answered Jun 18, 2019 at 10:39

Yksisarvinen

23.3k5 gold badges38 silver badges70 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Nikos C. Over a year ago

There doesn't need to be an std::begin and std::end for Container. If it has begin() and end() member functions, which any sane container type will have, std::begin and std::end will work.

eerorika Over a year ago

@NikosC. Well, if the container has those member functions, then there is std::begin and std::end for the container. That's why they work.

Nikos C. Over a year ago

@eerorika That's not correct. If you define your own container type, there is no std::begin overload or specialization for it. But it will work fine if your custom container has a begin() member function.

eerorika Over a year ago

@NikosC. There is an overload for the container. The specific template overload that returns c.begin().

Yksisarvinen Over a year ago

@Nicos Yes, I couldn't find the right wording to name it. C-style array has it's overloads, but for others it relies on existance of begin() and end() member methods. If you have better proposition, feel free to edit or suggest it in comments.

john · Accepted Answer · 2019-06-18 10:42:44Z

1

Templates let you write the function

template <class T, class U, size_t N>
bool in_array(const T& needle, U (&haystack)[N]) {
    // Check that type of needle matches type of array elements, then on check pass:
    return std::find(std::begin(haystack), std::end(haystack), needle) != std::end(haystack);
}

But I'm not really sure what this gets you, it's still statically typed. Static typing is a good thing of course.

Untested code.

edited Jun 18, 2019 at 10:42

answered Jun 18, 2019 at 10:39

john

88.3k5 gold badges61 silver badges95 bronze badges

1 Comment

john Over a year ago

@sp2danny Yes, but that was the question I think. Obviously the OP should be using proper C++ instead of trying to make C++ like PHP, but I'm just answering the question. I expect they'll realise the benefits of C++ soon enough.

Collectives™ on Stack Overflow

Is it possible to write an in_array helper function using std library's find, begin and end?

2 Answers 2

5 Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

5 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related