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Add

If you're familiar with Python, you'll be familiar with how Python objects can have an __add__ method. It allows developers to specify custom logic for different types of objects. For example, adding two integers we want to behave like this:

3 + 5
# 8

But with an array, we probably want it to work like this:

[3] + [5]
# [3, 5]

Assignment

This is the final lesson on objects, and it's a big one. Take your time – you'll be using a lot of the functions that you wrote in past chapters to complete this one.

Complete the snek_add function. It accepts two pointers to snek_object_t objects ("a" and "b") and returns a pointer to a new snek_object_t object (the result of the sum):

If either input is NULL, return NULL.
If "a" is an integer:
1. If "b" is an integer, return a new_snek_integer with the sum of the two integers.
2. If "b" is a float, return a new_snek_float with the sum of the integer and float.
3. Anything else, invalid operation, return NULL.
If "a" is a float:
1. If "b" is an integer, return a new_snek_float with the sum of the float and integer.
2. If "b" is a float, return a new_snek_float with the sum of the two floats.
3. Anything else, invalid operation, return NULL.
If "a" is a string:
1. If "b" is not a string, invalid operation, return NULL.
2. Otherwise:
  1. Calculate the length of the new string by combining the length of the two strings (properly handling the null terminator)
  2. Allocate memory for a new temporary string using calloc
  3. Use strcat to append the data from a and then b to the temporary string.
  4. Create a new_snek_string and pass in the temporary string.
  5. Free the memory for the temporary string and return the new string object.
If "a" is a vector3:
1. If "b" is not a VECTOR3, invalid operation, return NULL.
2. Otherwise:
  1. Create a new_snek_vector3.
  2. Recursively call snek_add for each of the x, y, and z fields. For example, a vector [1,2,3]+[4,5,6] should result in a new vector [5,7,9].
  3. Return the new vector struct.
If "a" is an array:
1. If "b" is not an array, invalid operation, return NULL.
2. Otherwise:
  1. Create a new_snek_array with the combined length of the two arrays.
  2. Iterate over each index in "a" and use snek_array_set and snek_array_get to copy the values from "a" to the new array.
  3. Do the same for "b".
  4. Return the new array object.
If "a" is none of the above, invalid operation, return NULL.

We won't implement subtract, multiply, or divide but each of these would follow the same pattern. This is how arithmetic operations work in Sneklang!