How to Write a Lambda Wrapping a Function with Optional Return Value

» cpp » How to Write a Lambda Wrapping a Function with Optional Return Value

By : An DaoDuc

Date : November 23 2020, 04:01 AM

This might help you I have tried to write a lambda that measures the execution time of arbitrary functions. With a lot of help I have managed that for C++14 and functions having a return value, see Measure execution time of arbitrary functions with C++14 lambda. , Use RAII instead for your timing:

code :

struct Timer
{
    explicit Timer(bool enable) : enable(enable)
    {
        if (enabled)
        {
            startTimePoint = std::chrono::steady_clock::now();
        }
    }

    ~Timer()
    {
        if (enabled)
        {
            const std::chrono::steady_clock::time_point stopTimePoint =
                    std::chrono::steady_clock::now();

            const std::chrono::duration<double> timeSpan =
                    std::chrono::duration_cast<std::chrono::duration<double>>(
                            stopTimePoint - startTimePoint);

            std::cout << taskName << " took " << timeSpan.count() << " seconds." <<
                    std::endl;
        }
    }

    Timer(const Timer&) = delete;
    Timer& operator=(const Timer&) = delete;

    bool enable;
    std::chrono::steady_clock::time_point startTimePoint;
};

template <typename Function, typename... Args>
auto measure(bool enabled, const std::string& taskName, Function&& function, Args&&... args)
->  decltype(std::forward<Function>(function)(std::forward<Args>(args)...))
{
    Timer timer(enabled);

    return std::forward<Function>(function)(std::forward<Args>(args)...);
}

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Anyway to make a (wrapping) NSTextField write a carriage return upon pressing return key?

By : AaronY_Pt

Date : March 29 2020, 07:55 AM

I wish did fix the issue. This is covered in Technical Q&A QA1454, which also enumerates reasons why one would use NSTextField instead of NSTextView in this case.
You can implement the following method in the text field delegate:

code :

- (BOOL)control:(NSControl*)control
    textView:(NSTextView*)textView
    doCommandBySelector:(SEL)commandSelector
{
    BOOL result = NO;

    if (commandSelector == @selector(insertNewline:))
    {
        // new line action:
        // always insert a line-break character and don’t cause the receiver
        // to end editing
        [textView insertNewlineIgnoringFieldEditor:self]; 
        result = YES;
    }

    return result;
}

lambda parameter with optional return value

By : Santhosh MP

Date : March 29 2020, 07:55 AM

seems to work fine Here's how I would implement for_almost_each; I'm using namespace std plus type aliases for readability purposes.

code :

#include <algorithm>
#include <iterator>
#include <functional>

using namespace std;

template<class Iter, class Func>
Iter
for_almost_each_impl(Iter begin, Iter end, Func func, std::true_type)
{
    for (auto i = begin; i!=end; ++i)
        if (!func(*i))
            return i;
    return end;
}

template<class Iter, class Func>
Iter
for_almost_each_impl(Iter begin, Iter end, Func func, std::false_type)
{
    for_each(begin, end, func);
    return end;
}


template<class Iter, class Func>
Iter for_almost_each(Iter begin, Iter end, Func func)
{
    using Val = typename iterator_traits<Iter>::value_type;
    using Res = typename result_of<Func(Val)>::type;
    return for_almost_each_impl(begin, end,
                                func,
                                is_convertible<Res, bool>{} );
}

How to invoke AWS lambda function from another lambda function and return without waitng for the called lambda result

By : S.Cardno

Date : March 29 2020, 07:55 AM

fixed the issue. Will look into that further With the AWS Lambda SDK for Java you can set the InvocationType within the InvokeRequest object. This will just invoke your function, but won't wait for a response.
From the Javadocs:

code :

AWSLambda lambdaClient = AWSLambdaClientBuilder.defaultClient();
InvokeRequest request = new InvokeRequest();
request.withFunctionName(name)
       .withInvocationType(InvocationType.Event)
       .withPayload(payload);
InvokeResult result = lambdaClient.invoke(request);

С++ wrapping lambda in another lambda inside a function

By : KOSHULAK

Date : March 29 2020, 07:55 AM

wish of those help The by-reference capture [&] causes the lambda to hold a reference to w after it has expired. You either need to copy w [=] or move it into the lambda (C++14):

code :

r.receive([w=std::move(w)]() {
    cout << "Before" << endl;   
    w();
    cout << "After" << endl;    
});

Lambda expression and Optional how to return String value

By : durgesh chander

Date : March 29 2020, 07:55 AM

around this issue Optional.ifPresent takes a Consumer - so you cannot return anything from it. Use Optional.map.

code :

Optional.ofNullable(MyObject.getPeople())
    .map(people -> people                                                                    
        .stream()                                                                    
        .filter(person -> person.getName().equals("test1"))
        .findFirst()
        .map(person -> person.getId()))
    .orElse(null);

Optional.ofNullable(MyObject.getPeople())
    .flatmap(people -> people                                                                    
        .stream()                                                                    
        .filter(person -> person.getName().equals("test1"))
        .findFirst()
        .map(person -> person.getId()));