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### 798. Refactoring of binders lead to interface breakage

Section: 99 [depr.lib.binders] Status: CD1 Submitter: Daniel Krügler Opened: 2008-02-14 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

N2521 and its earlier predecessors have moved the old binders from [lib.binders] to 99 [depr.lib.binders] thereby introducing some renaming of the template parameter names (`Operation -> Fn`). During this renaming process the protected data member `op` was also renamed to `fn`, which seems as an unnecessary interface breakage to me - even if this user access point is probably rarely used.

Proposed resolution:

Change [depr.lib.binder.1st]:

>     template <class Fn>
>     class binder1st
>       : public unary_function<typename Fn::second_argument_type,
>                               typename Fn::result_type> {
>     protected:
>       Fn fn op;
>       typename Fn::first_argument_type value;
>     public:
>       binder1st(const Fn& x,
>                 const typename Fn::first_argument_type& y);
>       typename Fn::result_type
>         operator()(const typename Fn::second_argument_type& x) const;
>       typename Fn::result_type
>         operator()(typename Fn::second_argument_type& x) const;
>     };

> > -1- The constructor initializes `fn` `op` with `x` and `value` with `y`.

> > -2- `operator()` returns `fnop(value,x)`.

Change [depr.lib.binder.2nd]:

>     template <class Fn>
>     class binder2nd
>       : public unary_function<typename Fn::first_argument_type,
>                               typename Fn::result_type> {
>     protected:
>       Fn fn op;
>       typename Fn::second_argument_type value;
>     public:
>       binder2nd(const Fn& x,
>                 const typename Fn::second_argument_type& y);
>       typename Fn::result_type
>         operator()(const typename Fn::first_argument_type& x) const;
>       typename Fn::result_type
>         operator()(typename Fn::first_argument_type& x) const;
>     };

> > -1- The constructor initializes `fn` `op` with `x` and `value` with `y`.

> > -2- `operator()` returns `fnop(value,x)`.