Question

Write a simple function template for predicate function isEqualto that compares its two arguments of the same type with the equality operator \((==)\) and returns true if they are equal and false if they are not equal. Use this function template in a program that calls isEqualto only with a variety of built-in types. Now write a separate version of the program that calls isEqualTo with a user-defined class type, but does not overload the equality operator. What happens when you attempt to run this program? Now overload the equality operator (with the operator function) operator==. Now what happens when you attempt to run this program?

Short answer

Initially, the program will not compile without overloaded `==`; it works after overloading operator.

Step-by-step solution

Define the Function Template

Start by defining a simple function template `isEqualto`. This function will take two parameters of the same type and return a boolean indicating whether or not they are equal. You can use the syntax: ```cpp template bool isEqualto(T a, T b) { return a == b; } ```

Test with Built-in Types

Create a program that tests the `isEqualto` function with different built-in types. For example: ```cpp #include int main() { int x = 5, y = 5; double a = 3.14, b = 3.14; char c = 'A', d = 'A'; std::cout << std::boolalpha; std::cout << "int comparison: " << isEqualto(x, y) << std::endl; std::cout << "double comparison: " << isEqualto(a, b) << std::endl; std::cout << "char comparison: " << isEqualto(c, d) << std::endl; return 0; } ```

Create a User-defined Class

Define a simple user-defined class without overloading the equality operator, such as: ```cpp class MyClass { public: int value; MyClass(int val) : value(val) {} }; ```

Call Function with User-defined Class

Try to call `isEqualto` with objects of `MyClass`. Note that this will result in a compilation error because the equality operator `==` is not overloaded for `MyClass` objects: ```cpp MyClass obj1(10), obj2(10); std::cout << "MyClass comparison: " << isEqualto(obj1, obj2) << std::endl; ``` The above code will not compile if `operator==` is not overloaded.

Overload the Equality Operator

Add an overloaded equality operator to `MyClass` so that it can be compared using `==`: ```cpp class MyClass { public: int value; MyClass(int val) : value(val) {} bool operator==(const MyClass& other) const { return this->value == other.value; } }; ```

Test with Overloaded Operator

Run the program again after overloading the equality operator. The `isEqualto` function should now work correctly with `MyClass` objects since the `==` operator is defined: ```cpp int main() { MyClass obj1(10), obj2(10); std::cout << "MyClass comparison: " << isEqualto(obj1, obj2) << std::endl; return 0; } } ``` The program compiles and accurately checks the equality.

Key concepts

Equality Operator Overloading

Overloading operators in C++, such as the equality operator \((==)\), allows custom types to have defined behaviors similar to built-in types. This means you can compare objects of a user-defined class just as effortlessly as basic types like integers or floats. However, to make this comparison possible, you need to explicitly define what equality means for that class.When you overload the equality operator in a user-defined class, you add a function to the class that dictates how two objects should be compared. Here’s how it typically works:

• The function is defined as a member function of the class.
• It takes a single argument, which is a constant reference to another object of the same class.
• The function returns a boolean, true if the two objects are considered equal and false otherwise.

A typical example might be:```cppbool operator==(const MyClass& other) const { return this->value == other.value;}```This allows the `isEqualto` template to operate with user-defined types, effectively treating them as if they were basic data types.

Built-in Types in C++

C++ provides several built-in types that form the basic types of data, ranging from integers to characters to floating points. These built-in types come with a pre-defined set of operations, including comparison, arithmetic, and logic. This is why when you write a function template like `isEqualto`, it can automatically handle any built-in type without additional operator overloading. Here's a quick look at some common built-in types:

• int: Represents whole numbers without any fractional component.
• double: Represents floating-point numbers, useful for computations with decimals.
• char: Used for storing individual characters, which can be combined into strings.

Functions that use built-in types operate straightforwardly, as these types already support operations like the equality operator. That's why the `isEqualto` function works flawlessly when comparing two `int`, `double`, or `char` variables. The beauty of built-in types is that since operations like equality are already defined for them, they integrate smoothly with function templates that expect these operations to work out-of-the-box.

User-defined Types

User-defined types in C++ allow developers to create custom data structures that fit specific needs, going beyond what built-in types offer. Classes and structs are the primary constructs used to define user-defined types.When creating a class, developers define both data (member variables) and behaviors (member functions) that the objects of this class can have. For instance, a `MyClass` with an integer member variable might represent an entity in your program with a specific value:```cppclass MyClass {public: int value; MyClass(int val) : value(val) {}};```Without operator overloading, functions like `isEqualto` can't compare objects of `MyClass` because the compiler doesn’t know how to interpret the \((==)\) operator for these objects. Unlike built-in types, user-defined types do not automatically support every operation.To leverage such user-defined types with templates effectively, you must provide implementations for operations that are necessary for the actions you intend to perform. This often involves overloading operators, like creating a sense of equality, comparison, or arithmetic operations, to allow user-defined types to behave as if they were built-in.