Why does a default argument for a lambda argument trigger a -pedantic" GCC warning?

Question

I had this lambda somewhere in my code:

[](bool a, bool=true){ return !a;} }

and GCC 4.6 \"complained\" with this warning:

warn         


        

Answer 1

Since C++14 it is allowed. It was found to be a defect long time ago: Default arguments for lambdas, and also Default arguments in lambda-expressions.

Answer 2

It makes no sense to have a default argument in a lambda function -- how could it ever be used? On the other hand, it does no harm, so why not allow it, after emitting a warning?

Answer 3

Section 5.1.2 paragraph 5 specifically says that you can not have default values for the parameters.

Default arguments (8.3.6) shall not be specified in the parameter-declaration-clause of a lambda-declarator.