Question

What is wrong with the syntax here? I follow this resource.

char x = 'a', y = 'a';

[&x,=y]() { // error: expected identifier before '=' token
  ++x; ++y; // error: 'y' is not captured
}();

I use MinGW g++ 4.5.2 command line compiler with -std=c++0x

clarification: I’d like to pass y by value.

Answer 1

char x = 'a', y = 'a';

[&x,y]() mutable{
  ++x; ++y;
}();

Live example.

Is the correct code. To capture a variably by-value, just write its name. To allow modification of by-value captures, the lambda needs to be marked mutable, otherwise the operator() is marked const.

§5.1.2 [expr.prim.lambda] p5

[…] This function call operator is declared const (9.3.1) if and only if the lambda-expression’s parameter-declaration-clause is not followed by mutable. […]