Category 

Type Trait Functions 

Syntax 

bool __has_trivial_default_constructor (typename T ) 

Returns true if and only if T has a trivial default constructor. 

Errorif T is an incomplete type. 

False (but well-formed) if a class type does not have a default constructor. 

According to the definition from Section 20.4.4.3 of the Working Draft notes, a type T has a trivial copy assignment operator if:

• a scalar type (or array thereof)
• an array of class type with a trivial default constructor
• a class type with a trivial default constructorr

According to Section 21.1 p5 of the Working Draft, a default constructor is trivial if:

• It is not user provided
• Its class has no virtual functions
• Its class has no virtual base classes
• Each direct base class of X has a trivial copy assignment operator.
• All the direct base classes of its class have trivial default constructors.
• For all the non-static data members of its class that are of class type (or array thereof), each such class has a trivial default constructor.

A default consructor is not user provided if it is implicitly declared, or defined inline as = default;. 

Ox interaction if the copy assign operator is defined as deleted. 

Ox interaction false if the default constructor is defined as deleted. 

Ox interaction with default function definitions.