CODEWITHSUNDEEP
c++boost-lambda
Abruzzo Forte e Gentile
Abruzzo Forte e Gentile

Reputation: 14869

return statement in lambda expression

I created a lambda expression inside my std::for_each call.

In it there is code like this one, but I have building error telling me that

error: expected primary-expression before ‘return’
error: expected `]' before ‘return’

In my head I think that boost-lambda works mainly with functors, so since return statement it isn't like that, calling it doesn't work.

Do you know what it is and how to fix it?

Thanks AFG

namespace bl = boost::lambda;
int a, b;
bl::var_type::type a_( bl::var( a ) );
bl::var_type::type b_( bl::var( b ) );

std::for_each( v.begin(), v.end(), (
// ..do stuff here
if_(  a_ > _b_ )
[
std::cout << _1,
 return
]
));

Upvotes: 2

Views: 959

Answers (3)

Barney Szabolcs
Barney Szabolcs

Reputation: 12524

@MBZ is right, use C++11 (but not lambda in this case).

Here is your code with C++11:

int a, b;
std::vector<int> v;
for(int e : v)
{
  if(a > b)
    std::cout << e;
}

Of course you could do the same with lambdas, but why complicating it like the code below?

int a, b;
std::vector<int> v;
std::for_each(v.begin(), v.end(), 
  [&a,&b](int e)
  {
    if(a > b)
      std::cout << e;
  }
);

Upvotes: 1

MBZ
MBZ

Reputation: 27612

just forget boost-lambda and use the new standard C++ lambda expression instead.

Explanation & Example

Upvotes: 4

Marc Andreson
Marc Andreson

Reputation: 3495

You cannot use return instruction inside lambda expression. Use constructions like if_then_else_return. They offer syntax that allows producing results. But in your case return is not even required, just throw it away.

Upvotes: 4

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