Styjun

Is Grandpa Irrational? Another Grandpa Mystery

Why did NASA use Imperial units?

USA: Can a witness take the 5th to avoid perjury?

What is the purpose of the fuel shutoff valve?

Why did modems have speakers?

Symbol of the tennis ball

I can't understand how 'static' works exactly

Why is chess failing to attract big name sponsors?

Why are angular mometum and angular velocity not necessarily parallel, but linear momentum and linear velocity are always parallel?

Direct revelation mechanism's sets of strategies and types

Grid/table with lots of buttons

How to repeat the last : command for a visual selection instead of whole buffer?

What is the meaning of "you has the wind of me"?

Do Rabbis get punished in Heaven for wrong interpretations or claims?

If my business card says 〇〇さん, does that mean I'm referring to myself with an honourific?

Spoken encryption

How can I receive packages while in France?

Why are line integrals not always path independent?

Impact of throwing away fruit waste on a peak > 3200 m above a glacier

What is the meaning of "a thinly disguised price"?

Why is a dedicated QA team member necessary?

401(k) investment after being fired. Do I own it?

Distribute large Tikz image on two A4 landscape

Do male skunks have teats?

Lambda copying a reference to a lambda reference VS2017 compile error

What is a lambda (function)?What are the differences between a pointer variable and a reference variable in C++?What is the difference between a 'closure' and a 'lambda'?Why are Python lambdas useful?Distinct() with lambda?list comprehension vs. lambda + filterWhat is the copy-and-swap idiom?What is a lambda expression in C++11?What is an undefined reference/unresolved external symbol error and how do I fix it?Compiling an application for use in highly radioactive environments

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;

7

2

Compiling the following code in Visual Studio 2017:

#include "pch.h"
#include <iostream>

int main()

 int test = 5;

 auto cb1 = [test]()
 
 auto cb2 = [&]()
 
 auto cb3 = [test]()
 
 std::cout << test;
 ;
 cb3();
 ;
 cb2();
 ;
 cb1();

Gives the compiler error

test.cpp(17): error C2440: '<function-style-cast>': cannot convert from 'const int' to 'main::<lambda_80fd0d4feae1377a5d8b8955e10105ab>::()::<lambda_38fc83ae6a7bd6540ebe1721869db4f1>'
test.cpp(17): note: No constructor could take the source type, or constructor overload resolution was ambiguous
test.cpp(18): error C3536: 'cb2': cannot be used before it is initialized
test.cpp(18): error C2064: term does not evaluate to a function taking 0 arguments

Does anybody know why Visual Studio gives this error? (it seem to compile ok on clang) You can get it to compile by replacing auto cb2 = [&]() with auto cb2 = [&test]() why does that fix the errors?

Even more interesting adding std::cout << test; or const int &ref = test; to the body of cb2 fixes the compiler error.

c++ lambda

share|improve this question

asked Mar 26 at 15:23

David FooksDavid Fooks

66888 silver badges1010 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Due to the fact, that G++ accepts such code, I suspect that it's a bug in VS2017, unless it's some form of UB, that I don't know about.
  
  – Algirdas Preidžius
  Mar 26 at 15:33
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Looks like MSVS isn't treating the treating the use of test in the capture of cb3 as a valid reason to capture test incb2. Not sure who is right in this case but I'm inclined to think the gcc is behaving correctly.
  
  – NathanOliver
  Mar 26 at 15:33
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I can reproduce this. My guess would be that the parser is confused about what [&] captures - it apparently tries to capture the implicit this (the cb1 instance that cb2 is in) on the one hand, but tries to initialize it with test directly. All your fixes probably alleviate that confusion. But in the end it's a bug in MSVC either way.
  
  – Max Langhof
  Mar 26 at 15:39
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Weird... Changing the lambda capture of cb3 to &test seems to do the job. rextester.com/FEFQ33220
  
  – Constantinos Glynos
  Mar 26 at 15:57
  
  

  
  
  
  

add a comment | 

7

2

Compiling the following code in Visual Studio 2017:

#include "pch.h"
#include <iostream>

int main()

 int test = 5;

 auto cb1 = [test]()
 
 auto cb2 = [&]()
 
 auto cb3 = [test]()
 
 std::cout << test;
 ;
 cb3();
 ;
 cb2();
 ;
 cb1();

Gives the compiler error

test.cpp(17): error C2440: '<function-style-cast>': cannot convert from 'const int' to 'main::<lambda_80fd0d4feae1377a5d8b8955e10105ab>::()::<lambda_38fc83ae6a7bd6540ebe1721869db4f1>'
test.cpp(17): note: No constructor could take the source type, or constructor overload resolution was ambiguous
test.cpp(18): error C3536: 'cb2': cannot be used before it is initialized
test.cpp(18): error C2064: term does not evaluate to a function taking 0 arguments

Does anybody know why Visual Studio gives this error? (it seem to compile ok on clang) You can get it to compile by replacing auto cb2 = [&]() with auto cb2 = [&test]() why does that fix the errors?

Even more interesting adding std::cout << test; or const int &ref = test; to the body of cb2 fixes the compiler error.

c++ lambda

share|improve this question

asked Mar 26 at 15:23

David FooksDavid Fooks

66888 silver badges1010 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Due to the fact, that G++ accepts such code, I suspect that it's a bug in VS2017, unless it's some form of UB, that I don't know about.
  
  – Algirdas Preidžius
  Mar 26 at 15:33
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Looks like MSVS isn't treating the treating the use of test in the capture of cb3 as a valid reason to capture test incb2. Not sure who is right in this case but I'm inclined to think the gcc is behaving correctly.
  
  – NathanOliver
  Mar 26 at 15:33
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I can reproduce this. My guess would be that the parser is confused about what [&] captures - it apparently tries to capture the implicit this (the cb1 instance that cb2 is in) on the one hand, but tries to initialize it with test directly. All your fixes probably alleviate that confusion. But in the end it's a bug in MSVC either way.
  
  – Max Langhof
  Mar 26 at 15:39
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Weird... Changing the lambda capture of cb3 to &test seems to do the job. rextester.com/FEFQ33220
  
  – Constantinos Glynos
  Mar 26 at 15:57
  
  

  
  
  
  

add a comment | 

Compiling the following code in Visual Studio 2017:

#include "pch.h"
#include <iostream>

int main()

 int test = 5;

 auto cb1 = [test]()
 
 auto cb2 = [&]()
 
 auto cb3 = [test]()
 
 std::cout << test;
 ;
 cb3();
 ;
 cb2();
 ;
 cb1();

Gives the compiler error

test.cpp(17): error C2440: '<function-style-cast>': cannot convert from 'const int' to 'main::<lambda_80fd0d4feae1377a5d8b8955e10105ab>::()::<lambda_38fc83ae6a7bd6540ebe1721869db4f1>'
test.cpp(17): note: No constructor could take the source type, or constructor overload resolution was ambiguous
test.cpp(18): error C3536: 'cb2': cannot be used before it is initialized
test.cpp(18): error C2064: term does not evaluate to a function taking 0 arguments

Does anybody know why Visual Studio gives this error? (it seem to compile ok on clang) You can get it to compile by replacing auto cb2 = [&]() with auto cb2 = [&test]() why does that fix the errors?

Even more interesting adding std::cout << test; or const int &ref = test; to the body of cb2 fixes the compiler error.

c++ lambda

share|improve this question

asked Mar 26 at 15:23

David FooksDavid Fooks

66888 silver badges1010 bronze badges

#include "pch.h"
#include <iostream>

int main()

 int test = 5;

 auto cb1 = [test]()
 
 auto cb2 = [&]()
 
 auto cb3 = [test]()
 
 std::cout << test;
 ;
 cb3();
 ;
 cb2();
 ;
 cb1();

test.cpp(17): error C2440: '<function-style-cast>': cannot convert from 'const int' to 'main::<lambda_80fd0d4feae1377a5d8b8955e10105ab>::()::<lambda_38fc83ae6a7bd6540ebe1721869db4f1>'
test.cpp(17): note: No constructor could take the source type, or constructor overload resolution was ambiguous
test.cpp(18): error C3536: 'cb2': cannot be used before it is initialized
test.cpp(18): error C2064: term does not evaluate to a function taking 0 arguments

share|improve this question

asked Mar 26 at 15:23

David FooksDavid Fooks

66888 silver badges1010 bronze badges

share|improve this question

asked Mar 26 at 15:23

David FooksDavid Fooks

66888 silver badges1010 bronze badges

asked Mar 26 at 15:23

David FooksDavid Fooks

66888 silver badges1010 bronze badges

asked Mar 26 at 15:23

David FooksDavid Fooks

66888 silver badges1010 bronze badges