Today let us try to understand the type trait std::is_trivial<T>. This trait checks if the given type is a trivial type. For a precise definition of what trivial means, please visit the official page.
As usual, we will go through three cases:
– Primitive types
– Classes without inheritance
– Classes involving inheritance
Case-1: Primitive Types
Take a look at the example below (as in the previous post, I am using the macro CHECK(T) to save some typing).
Primitive Types
The output is:
Program Output
For convenience, the expected output is shown commented alongside the code. It is interesting that lvalue and rvalue references are not considered trivial, but pointer type is.
Case-2: Classes without Inheritance
Let us look at the more interesting case involving classes. The image below shows different struct/class/union definitions.
User-defined Types
Class “A” has some instance variables and a member function. However, it does not have a constructor or destructor.
struct “B” does an inline initialization of a “const” field.
struct “C” defines a constructor but no destructor.
struct “D” defines a destructor but no constructor.
struct “E” defines an instance variable of user-defined type “A”.
“EArray” is a type that maps to an array of 10 elements of “E” type.
struct “F” declares a deleted assignment operator.
Finally, “U” is a union of three different types, one of which is a user-defined type “E”.
Here is the code that checks these types:
Example Program
What is the expected output? Here it is:
Program Output
Case-3: Classes Involving Inheritance
Our final example uses a few classes as part of inheritance. Take a look:
Inheritance Example
Here is the output from the program:
Program Output
The reason why “G” is not trivial is because it defines a virtual function. Since “H” derives from a trivial class “E” and adds nothing by itself, it is also a trivial type. Class “C” is not trivial and hence “I” is not trivial as well.
The above use cases cover the essential properties of is_trivial<T> trait. I hope you get the picture now.
You can download the source code from here.
Have a nice weekend!
Recent Comments