bslmf_isaccessiblebaseof

Detailed Description

Outline

• Purpose
• Classes
• Description
  • Usage
    • Example 1: Base And Derived Classes
    • Example 2: Unrelated Classes

Purpose

Provide a compile-time check for derived classes.

Classes

• bslmf::IsAccessibleBaseOf: meta-function for detecting derived classes

Description

This component provides a meta-function, bslmf::IsAccessibleBaseOf, that determines whether one class is an accessible base class of another class. The static constant bslmf::IsAccessibleBaseOf::value is true if the template parameter t_BASE class is an accessible base class of, or the same class as, the template parameter t_DERIVED. Otherwise, bslmf::IsAccessibleBaseOf::value is false. The specific cases of private, protected, and ambiguous inheritance are not supported for versions of C++ prior to 11.

Usage

In this section we show intended use of this component.

Example 1: Base And Derived Classes

Define two classes, one inheriting from the other.

struct Base
{};
 
struct Derived : Base
{};

Evaluate bslmf::IsAccessibleBaseOf::value.

void example1()
{
    assert((true  == bslmf::IsAccessibleBaseOf<Base,    Derived>::value));
    assert((true  == bslmf::IsAccessibleBaseOf<Base,    Base>   ::value));
    assert((true  == bslmf::IsAccessibleBaseOf<Derived, Derived>::value));
    assert((false == bslmf::IsAccessibleBaseOf<Derived, Base>   ::value));
}

Example 2: Unrelated Classes

Define two classes, one inheriting privately from the other.

class Unrelated
{};
 
class Unrelated2
{};

Evaluate bslmf::IsAccessibleBaseOf::value. Note that Derived is not observably derived from Base, so std::is_base_of would evaluate true, but bslmf::IsAccessibleBaseOf evaluates false.

void example2()
{
    assert((false ==
            bslmf::IsAccessibleBaseOf<Unrelated, Unrelated2>::value));
}