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C++20 gives us the spaceship operator and even allows us to default it, generating all comparisons with default semantics, which will remove a lot of boilerplate from our code bases, great!
But how about equality and inequality? Does C++20 also give us a way to default equality and inequality? According to cppreference.com, defaulting spaceship will only give us So, is there a way to also (or only) default generate < <= >, and >=, but not == and !=. Given that I usually need equality/inequality way more often than greater/less, this seems to be quite unfortunate.== and != in C++20?
Update: The page now contains a description for defaulting operator==. Seems that I accessed the page like two hours before the documentation for this was added. :D
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Checking for equality in C and C++identifier == identifier; The == sign is used to compare primitive types such as char, int, float, etc. The comparison operator returns true if the two identifiers are equal.
The equality operator (==) is used to compare two values or expressions. It is used to compare numbers, strings, Boolean values, variables, objects, arrays, or functions.
The equality operators in C++ are is equal to(==) and is not equal to(!=). They do the task as they are named. The binary equality operators compare their operands for strict equality or inequality. The equality operators, equal to (==) and not equal to (!
Inequality operator != The inequality operator != returns true if its operands are not equal, false otherwise. For the operands of the built-in types, the expression x != y produces the same result as the expression ! (x == y). For more information about type equality, see the Equality operator section.
In C++20, if we use the default <=>, then all the other comparison operators are also added. Here in the code the class has two integers so to compare there would be user-defined comparison required. But since the equality operator will be generated automatically, I need to know how it will compare the objects.
The relational and equality operators test the following relationships: The first four operators in the list above have a higher precedence than the equality operators ( == and != ). See the precedence information in the table Precedence and Associativity of C Operators. The operands can have integral, floating, or pointer type.
The equality comparison function (whether defaulted or not) is called whenever values are compared using == or != and overload resolution selects this overload. Like defaulted special member functions, a defaulted comparison function is defined if odr-used or needed for constant evaluation .
Does C++20 also give us a way to default equality and inequality?
Yes (but see the last paragraph). The syntax is same:
friend bool operator==(const T&, const T&) = default;
friend bool operator!=(const T&, const T&) = default; // not needed if == exists
The ordered inequality can be defaulted also:
friend bool operator<=(const T&, const T&) = default;
// ...
defaulting spaceship will only give us
<<=>, and>=, but not==and!=
This is inaccurate. Defaulting three way comparison gives us all comparisons So, the above are not needed in that case.
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