return statement in lambda expression

Question

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
]
));

Marc Andreson · Accepted Answer · 2010-07-22 14:53:07Z

4

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.

answered Jul 22, 2010 at 14:53

Marc Andreson

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MBZ · Accepted Answer · 2010-07-22 14:55:54Z

4

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

Explanation & Example

answered Jul 22, 2010 at 14:55

MBZ

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1 Comment

Barney Szabolcs Over a year ago

Actually he better does not use lambdas here, check my answer.

Barney Szabolcs · Accepted Answer · 2012-12-03 04:45:20Z

1

@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;
  }
);

edited Dec 3, 2012 at 4:45

answered Dec 3, 2012 at 4:40

Barney Szabolcs

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