Constructor Specifiers

• explicit
• mutable
• delete
• default

Original Code

What The Compiler Does

Problem

• Compiler can perform a single implicit conversion to get a type
• Any single parameter constructors can be automatically called to get the type of an argument
• Single-parameter constructor Buffer(int n) is being used

Why?

Use of explicit

Use of explicit

explicit Notes

• The explicit specifier prevents the compiler from using that constructor for implicit conversion
• Consider a good practice of always using explicit on single-parameter constructors until it causes a problem

Code

Code Error

Use of mutable

mutable Notes

• Data members with mutable can change and still allow the object to be const
• bitwise const
• Not a single bit can change
• logical const
• The behavior of the object does not change
• bitwise const implies logical const

Constructor Scenario

Class I

• Implicit default constructor: A::A()
• Implicit copy constructor: A::A(const A&)
• Implicit assignment operator: A::operator=(const A&)

Class II

Class II Error

Class II

• Implicit copy constructor: A::A(const A&)
• Implicit assignment operator: A::operator=(const A&)
• Implicit default constructor: A::A()

Class II A()

Class II default

default

• Indicates that the compiler-provided constructor is used, even if it does not appear according to the constructor rules
• Can be applied to other constructors, standard methods, and destructors

POD: Plain Old Data

• A POD class (or struct) is a set of values without any object-oriented features (no vtable, for example)
• All scalar types (e.g., int, double) are POD
• POD class:
• Has no user-defined copy assignment operator
• Has no user-defined destructor
• Has no non-static data members that are not themselves POD
• Does not use virtual

default vs {}

Full Application of default

POD with default

delete

Error

delete