[PATCH] Implement std::experimental::sample

[Eric Fiselier]

In http://reviews.llvm.org/D9044#156827, @eugenis wrote:

> In http://reviews.llvm.org/D9044#156813, @EricWF wrote:
>
> > You'll need to use reserved identifiers
>
>
> Do you mean for local variable names? Is there a technical reason for this, or just a code style thing?


For any name not defined in the standard you should use reserved identifiers. Assume that the user of the standard library defines every non-reserved, non-defined name as a macro. We use reserved identifiers so that conforming programs can define non-reserved names globally and still use the standard library.

For example:

  #define PopulationIterator char*
  #define SampleIterator char*
  #define UniformRandomNumberGenerator &rand
  #include <experimental/algorithm>



> > and guard the definition of `sample` inside a C++14 only block because adding a new definition of could break existing code.

> 

> 

> n4335 does not seem to require that this is only available in C++14. And aren't names under std:: already reserved, and an addition of a new std:: name could not break compliant code?


I would prefer not to restrict these things to c++14 only, although there may be a reason that conforming implementations need to that isn't visible in n4335.

However because `sample` is a function it can be looked up by ADL. Since `sample` takes user-defined iterator types and RNG's it is possible that existing unqualified calls to `sample` in user code may now find `std::sample`.


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