How to return a lambda function?

Question

For example, I can define a lambda function as

auto f = [](double value) {double ratio = 100; return value * ratio;}

Now I want to generate a function with the ratio an argument and return the lambda function like

auto makeLambda(double ratio) { return [=](double value) {return value * ratio;}; }

How to do it?

Answer 1

With C++14 function return type deduction, that should work.

In C++11, you could define another lambda (which can deduce the return type), rather than a function (which can't):

auto makeLambda = [](double ratio) {
    return [=](double value) {return value * ratio;};
};

As noted in the comments, this could be further wrapped, if you particularly want a function:

auto makeLambdaFn(double ratio) -> decltype(makeLambda(ratio)) {
    return makeLambda(ratio);
}