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Avoiding Implicit Conversion in Constructor. Explicit keyword doesn't help here

What does the explicit keyword mean?Can you use keyword explicit to prevent automatic conversion of method parameters?Can a single argument constructor with a default value be subject to implicit type conversionwhy constructors aren't explicit by default?What could go wrong if copy-list-initialization allowed explicit constructors?Explicit conversion functions, direct-initialization, and converting constructorsHow to provide implicit and explicit conversion ctr for same type?Implicit conversion from user-defined type to primitive type in C++Is list-initialization an implicit conversion?How to combine type constraints & implicit conversions with C++11 universal references?

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8

1

I am able to avoid the implicit conversion of constructor using explicit keyword. So now, conversions like A a1 = 10; can be avoided.

But still I can initialize A a1 = A(20.2);. How can I disable the object creation such that only object can be created if we pass integer as a parameter e.g. A a1 = A(10)?

#include <iostream>

class A

public :
 explicit A(int a)
 
 num = a;
 

 int num;
;

int main()

 A a1=A(10.0);
 std::cout << a1.num;
 return 0;

c++ c++11

share|improve this question

edited 8 hours ago

YSC

27.1k66 gold badges5959 silver badges114114 bronze badges

asked 8 hours ago

Gurpreet DhamiGurpreet Dhami

5133 bronze badges

add a comment | 

8

1

I am able to avoid the implicit conversion of constructor using explicit keyword. So now, conversions like A a1 = 10; can be avoided.

But still I can initialize A a1 = A(20.2);. How can I disable the object creation such that only object can be created if we pass integer as a parameter e.g. A a1 = A(10)?

#include <iostream>

class A

public :
 explicit A(int a)
 
 num = a;
 

 int num;
;

int main()

 A a1=A(10.0);
 std::cout << a1.num;
 return 0;

c++ c++11

share|improve this question

edited 8 hours ago

YSC

27.1k66 gold badges5959 silver badges114114 bronze badges

asked 8 hours ago

Gurpreet DhamiGurpreet Dhami

5133 bronze badges

add a comment | 

I am able to avoid the implicit conversion of constructor using explicit keyword. So now, conversions like A a1 = 10; can be avoided.

But still I can initialize A a1 = A(20.2);. How can I disable the object creation such that only object can be created if we pass integer as a parameter e.g. A a1 = A(10)?

#include <iostream>

class A

public :
 explicit A(int a)
 
 num = a;
 

 int num;
;

int main()

 A a1=A(10.0);
 std::cout << a1.num;
 return 0;

c++ c++11

share|improve this question

edited 8 hours ago

YSC

27.1k66 gold badges5959 silver badges114114 bronze badges

asked 8 hours ago

Gurpreet DhamiGurpreet Dhami

5133 bronze badges

#include <iostream>

class A

public :
 explicit A(int a)
 
 num = a;
 

 int num;
;

int main()

 A a1=A(10.0);
 std::cout << a1.num;
 return 0;

share|improve this question

edited 8 hours ago

YSC

27.1k66 gold badges5959 silver badges114114 bronze badges

asked 8 hours ago

Gurpreet DhamiGurpreet Dhami

5133 bronze badges

share|improve this question

edited 8 hours ago

YSC

27.1k66 gold badges5959 silver badges114114 bronze badges

asked 8 hours ago

Gurpreet DhamiGurpreet Dhami

5133 bronze badges

edited 8 hours ago

YSC

27.1k66 gold badges5959 silver badges114114 bronze badges

edited 8 hours ago

YSC

27.1k66 gold badges5959 silver badges114114 bronze badges

asked 8 hours ago

Gurpreet DhamiGurpreet Dhami

5133 bronze badges

asked 8 hours ago

Gurpreet DhamiGurpreet Dhami

5133 bronze badges

3 Answers
3

active

oldest

votes

14

You can delete A::A(<anything not an int>);:

struct A

 explicit A(int a)
 : num(a)
 

 template<class T>
 A(T) = delete;

 int num;
;

int main()

 //A a1=A(10.0); // error: use of deleted function 'A::A(T) [with T = double]'
 A a2 = A(10); // OK
 (void) a2;

Demo: https://coliru.stacked-crooked.com/a/425afc19003697c9

share|improve this answer

answered 8 hours ago

YSCYSC

27.1k66 gold badges5959 silver badges114114 bronze badges

add a comment | 

7

The way to achieve this is to provide another constructor that would be a better match, and then delete it so you'll get an error. For your class, adding

template <typename T>
A(T) = delete;

Will stop the class from being constructed from anything that isn't an int

share|improve this answer

answered 8 hours ago

NathanOliverNathanOliver

110k1919 gold badges167167 silver badges246246 bronze badges

add a comment | 

3

Explicitly delete the constructor for double (possibly add float):

A(double) = delete;

share|improve this answer

answered 8 hours ago

Sombrero ChickenSombrero Chicken

27.4k33 gold badges3636 silver badges8585 bronze badges

add a comment | 

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14

You can delete A::A(<anything not an int>);:

struct A

 explicit A(int a)
 : num(a)
 

 template<class T>
 A(T) = delete;

 int num;
;

int main()

 //A a1=A(10.0); // error: use of deleted function 'A::A(T) [with T = double]'
 A a2 = A(10); // OK
 (void) a2;

Demo: https://coliru.stacked-crooked.com/a/425afc19003697c9

share|improve this answer

answered 8 hours ago

YSCYSC

27.1k66 gold badges5959 silver badges114114 bronze badges

add a comment | 

14

You can delete A::A(<anything not an int>);:

struct A

 explicit A(int a)
 : num(a)
 

 template<class T>
 A(T) = delete;

 int num;
;

int main()

 //A a1=A(10.0); // error: use of deleted function 'A::A(T) [with T = double]'
 A a2 = A(10); // OK
 (void) a2;

Demo: https://coliru.stacked-crooked.com/a/425afc19003697c9

share|improve this answer

answered 8 hours ago

YSCYSC

27.1k66 gold badges5959 silver badges114114 bronze badges

add a comment | 

You can delete A::A(<anything not an int>);:

struct A

 explicit A(int a)
 : num(a)
 

 template<class T>
 A(T) = delete;

 int num;
;

int main()

 //A a1=A(10.0); // error: use of deleted function 'A::A(T) [with T = double]'
 A a2 = A(10); // OK
 (void) a2;

Demo: https://coliru.stacked-crooked.com/a/425afc19003697c9

share|improve this answer

answered 8 hours ago

YSCYSC

27.1k66 gold badges5959 silver badges114114 bronze badges

struct A

 explicit A(int a)
 : num(a)
 

 template<class T>
 A(T) = delete;

 int num;
;

int main()

 //A a1=A(10.0); // error: use of deleted function 'A::A(T) [with T = double]'
 A a2 = A(10); // OK
 (void) a2;

share|improve this answer

answered 8 hours ago

YSCYSC

27.1k66 gold badges5959 silver badges114114 bronze badges

answered 8 hours ago

YSCYSC

27.1k66 gold badges5959 silver badges114114 bronze badges

answered 8 hours ago

YSCYSC

27.1k66 gold badges5959 silver badges114114 bronze badges

7

The way to achieve this is to provide another constructor that would be a better match, and then delete it so you'll get an error. For your class, adding

template <typename T>
A(T) = delete;

Will stop the class from being constructed from anything that isn't an int

share|improve this answer

answered 8 hours ago

NathanOliverNathanOliver

110k1919 gold badges167167 silver badges246246 bronze badges

add a comment | 

7

The way to achieve this is to provide another constructor that would be a better match, and then delete it so you'll get an error. For your class, adding

template <typename T>
A(T) = delete;

Will stop the class from being constructed from anything that isn't an int

share|improve this answer

answered 8 hours ago

NathanOliverNathanOliver

110k1919 gold badges167167 silver badges246246 bronze badges

add a comment | 

The way to achieve this is to provide another constructor that would be a better match, and then delete it so you'll get an error. For your class, adding

template <typename T>
A(T) = delete;

Will stop the class from being constructed from anything that isn't an int

share|improve this answer

answered 8 hours ago

NathanOliverNathanOliver

110k1919 gold badges167167 silver badges246246 bronze badges

template <typename T>
A(T) = delete;

share|improve this answer

answered 8 hours ago

NathanOliverNathanOliver

110k1919 gold badges167167 silver badges246246 bronze badges

answered 8 hours ago

NathanOliverNathanOliver

110k1919 gold badges167167 silver badges246246 bronze badges

answered 8 hours ago

NathanOliverNathanOliver

110k1919 gold badges167167 silver badges246246 bronze badges

3

Explicitly delete the constructor for double (possibly add float):

A(double) = delete;

share|improve this answer

answered 8 hours ago

Sombrero ChickenSombrero Chicken

27.4k33 gold badges3636 silver badges8585 bronze badges

add a comment | 

3

Explicitly delete the constructor for double (possibly add float):

A(double) = delete;

share|improve this answer

answered 8 hours ago

Sombrero ChickenSombrero Chicken

27.4k33 gold badges3636 silver badges8585 bronze badges

add a comment | 

Explicitly delete the constructor for double (possibly add float):

A(double) = delete;

share|improve this answer

answered 8 hours ago

Sombrero ChickenSombrero Chicken

27.4k33 gold badges3636 silver badges8585 bronze badges

A(double) = delete;

share|improve this answer

answered 8 hours ago

Sombrero ChickenSombrero Chicken

27.4k33 gold badges3636 silver badges8585 bronze badges

answered 8 hours ago

Sombrero ChickenSombrero Chicken

27.4k33 gold badges3636 silver badges8585 bronze badges

answered 8 hours ago

Sombrero ChickenSombrero Chicken

27.4k33 gold badges3636 silver badges8585 bronze badges