In UE4C, the Rider editor will prompt me that this variable can be set as a constant. Why must I do this? This increases the amount of code. Although it improves robustness, my subsequent code will not modify this variable.

Setting variables as constants (const) is a good programming practice and helps make your code more readable and maintainable. Although it may add some code size, the benefits usually outweigh this small overhead. Here are some reasons:

Although using constants may increase the size of your code slightly, it is generally considered a good programming practice and helps improve the quality and maintainability of your code. Of course, specific decisions also depend on the coding standards of the project and team, as well as the specific situation. If you are sure that a variable will never be modified, declaring it as a constant is a good choice.

double UVerticalCurveAlgorithm::Calcuate_GetElevetion_Grade(FVerticalCurveData InVerticalCurveData_01, FVerticalCurveData InVerticalCurveData_02, double InMileage)

Similarly, the compiler prompted me to consider passing formal parameters as constant references. Is it considered that this code does not need to copy the parameters every time it is called?

Compiler prompts to use constant reference to pass formal parameters are usually to improve performance and avoid unnecessary object copying. In your function signature, InVerticalCurveData_01 and InVerticalCurveData_02 are parameters of structure type. If the structure is large, object copying will occur when passed to the function, and using constant references can avoid this copying.

Rewrite your function declaration to use constant reference parameters. Consider writing it like this:

Such rewriting not only avoids object copying, but also expresses a message: these two structure parameters will not be modified inside the function.

It should be noted that there are conditions for passing structure parameters using constant references. This rewriting may not always be beneficial if the structure object is small, the overhead of object copying is not large, or if the parameters really need to be modified inside the function. When it comes to performance optimization, it's best to test and evaluate on a case-by-case basis.

For parameters of basic data types (such as double), there is usually no need to change them to constant references because their size is small and the performance overhead when passing them is relatively small. Constant references are mainly used for passing large objects (such as structures or classes).