How can I apply functions to elements of a tuple of vectors using template programming in C ?

Using Templates to Call Functions on Tuple Elements

In scenarios where you have a tuple of vectors and desire to execute a specific function on each vector element, the question arises as to how to achieve this efficiently. This article provides a comprehensive solution utilizing template functions and meta-programming techniques to address this challenge.

The template struct TupleOfVectors stores a tuple of vectors and defines a member function do_something_to_each_vec. Within this function, the goal is to iteratively call a function do_something_to_vec on each vector within the tuple using compile-time indices.

Indices Machinery with gen_seq and seq

To handle the iteration, we employ the gen_seq meta-function to generate compile-time integer sequences and utilize the seq class to represent those sequences. This enables the runtime generation of index values.

Function Templates for Iteration

Next, we introduce two function templates: for_each and for_each_in_tuple. for_each utilizes the indices generated by gen_seq to perform a loop over the tuple elements, executing the provided function f on each element and storing the results in a tuple. for_each_in_tuple simplifies the process, providing a convenient way to iterate over the elements of a tuple and invoke the specified function.

Usage Example

To illustrate the usage of these functions, consider the following example:

<code class="cpp">std::tuple<int, double, std::string> t(42, 3.14, "Hello World!");
for_each_in_tuple(t, my_functor());</code>

In this code, a tuple is created with three elements. The for_each_in_tuple function is called with this tuple and a lambda function my_functor that simply prints each element.

Specific Solution for TupleOfVectors

Returning to the original problem, we can incorporate these techniques into the TupleOfVectors struct by defining a tuple_vector_functor that operates on each vector. do_something_to_each_vec then invokes for_each_in_tuple with this functor to achieve the desired functionality.

Updates for C 14 and Later

For C 14 and up, std::integer_sequence can replace the custom seq and gen_seq classes for more concise code.

C 17 Option

In C 17 and later, the std::apply function can further simplify the code, reducing it to a single line of code that efficiently applies the desired function to the tuple elements.

In conclusion, this in-depth response provides a versatile approach to the problem of applying functions to tuple elements, addressing various C versions. The techniques employed empower developers to handle such scenarios efficiently and flexibly.

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