P0608r3, as adopted in San Diego 2018,  addresses several surprising type conversion choices that occur during overload resolution in the use of std::variant.

 

However, that has led to a split between how things end up working between "classic" overload resolution, and overload resolution for std::variant. It feels like this was not the intent, and certainly leads to a how-to-teach problem.

 

For instance.

 

 

Before P0608 - behaviour is consistent, but surprising

 

int func( string )

{

   return 42;

}

 

int func( bool )

{

   return 19;

}

 

int x = func( "Hello" );   // x is 19

int y= func( "Hello"s );  // x is 42

 

std::variant< bool, string > z;

z = "Hello World";          // z holds a bool

 

Now, with P0608 in place, we have conflicting behaviour, but the variant case is "sane".

int func( string )

{

   return 42;

}

 

int func( bool )

{

   return 19;

}

 

int x = func( "Hello" );   // x is 19

int y= func( "Hello"s );  // x is 42

 

std::variant< bool, string > z;

z = "Hello World";          // z holds a string

 

Given where we are in the cycle, I don't know if the correct thing to do is to suggest that we fix the core language, undo P0608, do nothing, or some fourth option.

 

Kind Rgds

Staffan Tj.

 




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