C++ Operators

C++ supports a lot of operators! These include operators that easily come to mind such as arithmetic and logical operators, as well as conversion operators. It also includes obscure operators you probably do not use much (comma operator?).

Both C++ and Ruby support operator overriding, although C++ supports more of them. The sections below describe how to map C++ operators to Ruby operators.

C++ operators that are not supported by Ruby can be mapped to Ruby methods instead. By convention these methods are named based on the C++ operator name. Thus the C++ assign operator, =, is mapped to a Ruby method called assign.

my_object1 = SomeClass.new
my_object2 = SomeClass.new
my_object1.assign(my_object2)

Arithmetic Operators

C++ and Ruby support overriding the same arithmetic operators.

C++	Ruby
+	+
-	-
*	*
/	/
%	%

Assignment Operators

C++ supports overriding assignment operators while Ruby does not. Thus these operators must be mapped to Ruby methods.

C++	Ruby	Ruby Method
=	Not overridable	assign
+=	Not overridable	assign_plus
-=	Not overridable	assign_minus
*=	Not overridable	assign_multiply
/=	Not overridable	assign_divide
%=	Not overridable	assign_plus

Bitwise Operators

C++ and Ruby support overriding the same bitwise operators.

C++	Ruby
&	&
|	|
~	~
<<	<<
>>	>>

Comparison (Relational) Operators

C++ and Ruby support overriding the same comparison operators.

C++	Ruby
==	==
!=	!=
>	<
<	>
>=	>=
<=	<=

Logical Operators

Ruby allows the ! operator to be overridden but not && or ||.

C++	Ruby	Ruby Method
&&	Not overridable	logical_and
||	Not overridable	logical_or
!	!	decrement_pre

Increment / Decrement Operators

C++ supports increment and decrement operators while Ruby does not. Thus these operators must be mapped to Ruby methods.

C++	Ruby	Ruby Method
++a	Not overridable	increment_pre
a++	Not overridable	increment
–a	Not overridable	decrement_pre
a–	Not overridable	decrement

Other Operators

C++ and Ruby support overriding an additional set of operators. The comma operator is not overridable in Ruby nor does it make sense to map it to a Ruby method.

C++	Ruby	Ruby Method
[]	[]
	[]= (if reference)
()	Not Overridable	call
*	Not Overridable	dereference
<<	<<
>>	>>
,	Not overridable

If a C++ class defines an [] operator that returns a reference, then in it should be mapped to two Ruby operators: [] and []=.

C++ classes that support the () operator are known as functors. Ruby supports overriding the .() operator by defining a call function. Note this isn’t quite the same as C++ because it is invoked via .() and not () – notice the . before the ().

Conversion Operators

C++ allows users to define explicit and implicit conversion operators or functions. These are used to convert a class to a different types. For example:

class Money
{
public:
    Money(float amount);
    operator float() const;
};

The operator double() const; is a user defined conversion function that converts a Money instance to a double. Following Ruby conventions, these conversion functions should be exposed as to_ method, in this case to_f.