Under the hood of C++ lambdas and std::function

Re:Under the hood of C++ lambdas and std::function by Kristine1975 on Monday March 28, 2016 @05:59AM (#11373439)

It's also wrong. If the compiler inlines e.g. std::sort, it doesn't matter whether the comparator is a lambda or a pointer to a function: The compiler knows what it is and can inline it as well. The only exception is when the function is defined in a different compilation unit. Then the compiler has no access to its definition and thus cannot inline it into std::sort.

The "C++ with lambda is faster than C with function" comes from C's qsort function that takes a function pointer to a comparator and is not inlined by the compiler. This can result in it being slower than std::sort.

BTW since lambdas without capture decay to function pointers, you can pass such a lambda to qsort.

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Re:Under the hood of C++ lambdas and std::function by gpderetta on Monday March 28, 2016 @02:32PM (#11376243)

In principle there is no difference, in practice until relatively recently some popular compilers would fail to inline calls via function pointers. The reason is that the inliner would need to run after constant propagation and after the HOF function itself, i.e. sort, has been inlined. With function objects and templates you get a distinct instance of sort for each callback type so the target is known statically even before any optimisation starts.

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