Thread: Lambdas, why are they so confusing?

Originally Posted by MutantJohn

It's like the creators of c++11 standard wanted to make it seem convoluted.

They just continue the tradition of the language creator.

Stroutstrup's main goal was to create such complex language, that programmers would always have work supporting code written in it.

I don't find lambdas difficult at all. apart from the capture clause, their syntax is quite like the rest of C++. it's a new major feature of the language. you can't expect to be fully comfortable with it overnight. just play with them and learn as much as you can. you'll eventually get to the point where it's just as natural to write them as any other part of the language.

The lambda allows you to write a functor inline, so that the code of the functor is found at the same spot where the functor is used. Before lambdas, functors had to be implemented as classes elsewhere in the source code, making it hard to know what the functor does without scrolling away to another section of code.

That's really all they're for. You can achieve all the same things a lambda does without using lambda, it's just not as nice.

Originally Posted by brewbuck

The lambda allows you to write a functor inline, so that the code of the functor is found at the same spot where the functor is used. Before lambdas, functors had to be implemented as classes elsewhere in the source code, making it hard to know what the functor does without scrolling away to another section of code.

That's really all they're for. You can achieve all the same things a lambda does without using lambda, it's just not as nice.

Yep, they're especially useful for situations where you need to do some repetitive task within a function.

Code:

#include <iostream>
void wtf( int arg )
{
    std::cout << arg << " - WTF?!!!" << std::endl;
}
int fun( int value )
{
    int result = 390937;
    auto cleanup = [&result, value]( )
    {
        result = 0;
        wtf( value );
    };    
    if( value < 314821 )
        cleanup( );
    else if( value > 357761 )
        cleanup( );
    else
        result *= value;
    return result;
}
int main( )
{
    fun( 280601 );
}

Achieving something like that was always such a pain in the arse with C++03...

Originally Posted by Sebastiani

Achieving something like that was always such a pain in the arse with C++03...

Your example is not particularly illustrative of anything except poor coding style. This version (without lambda) is much cleaner than your version

Code:

int fun( int value )
{
    int result = 0;
    if ( value < 314821 || value > 357761 )
         wtf(value);
    else
        result = 390937 * value;
    return result;
}

Of course, the usage of magic values is poor style, but that's unrelated to your point or mine.

Originally Posted by grumpy

Your example is not particularly illustrative of anything except poor coding style. This version (without lambda) is much cleaner than your version

Please try to understand that it was just an abstract example, grumpy. I imagine that must be very hard for your pedantic mind to grasp, but I'm sure that with a little effort even you can appreciate the point of the demonstration.

Originally Posted by grumpy

Of course, the usage of magic values is poor style, but that's unrelated to your point or mine.

Rather, since the numbers are meaningless in the context of the example given, assigning labels to them would only serve to confuse the reader into thinking that the actual values were somehow tied to the point being made. Otherwise I most certainly would have given them concrete names, such as "A001262_26" and so forth...

I'd say that a fairly common use case would be specifying a predicate when using various standard algorithms.

I thought predicate technically meant a boolean function.
(Or is that just lisp terminology? ..where appending _p after a function signifies that it is a yes/no question.)