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c++c++11lambdamovervalue-reference
Francis Moy
Francis Moy

Reputation: 195

Understanding Move Capture in Lambdas for C++11

I have a question regarding the workaround proposed in order to address move capture in C++11 lambdas. In particular, taking the example from Meyer's book: 

std::vector<double> data;
... 
auto func = std::bind( [](const std::vector<double>& data) 
                       { /*uses of data*/ },
                       std::move(data)
                     );

My question is: what would be the consequences/meaning of declaring the parameter "data" as an rvalue reference?:

auto func = std::bind( [](std::vector<double>&& data)
...

To help you guide the answer, I'll make three claims. Please tell me if I'm right or wrong:

Thanks in advance.

Upvotes: 3

Views: 940

Answers (1)

T.C.
T.C.

Reputation: 137310

what would be the consequences/meaning of declaring the parameter "data" as an rvalue reference?

It won't compile (at least if you attempt to actually call func). std::bind always pass bound arguments as lvalues, which won't bind to the rvalue reference.

In both cases, it is not safe to use data after the definition of "func".

data is left in a valid but unspecified state by the move. You can use it the same way you use a vector whose contents are unknown.

Upvotes: 6

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