| Home | Libraries | People | FAQ | More

## Struct template call_if_statement<true, Then, ThenResult>

boost::contract::call_if_statement<true, Then, ThenResult> — Template specialization to handle static predicates that are `true` for then-branch functor template calls that do not return void (not needed on C++17 compilers, use `if constexpr` instead).

## Synopsis

    // In header: <boost/contract/call_if.hpp>

    template<typename Then, typename ThenResult>
    struct call_if_statement<true, Then, ThenResult> {

      // public member functions
      explicit call_if_statement(Then);
      operator ThenResult() const;
      template<typename Else> ThenResult else_(Else const &) const;
      template<bool ElseIfPred, typename ElseIfThen>
        call_if_statement< true, Then, ThenResult >
        else_if_c(ElseIfThen const &) const;
      template<typename ElseIfPred, typename ElseIfThen>
        call_if_statement< true, Then, ThenResult >
        else_if(ElseIfThen const &) const;
    };

## Description

Usually this class template is instantiated only via the return value of `boost::contract::call_if` and `boost::contract::call_if_c`.

See Also: Assertion Requirements

### Template Parameters

1.     typename Then

   Type of functor template to call when the static predicate is `true` (as it is for this template specialization).

2.     typename ThenResult

   Non-void return type of the then-branch functor template call.

### `call_if_statement` public member functions

1.     explicit call_if_statement(Then f);

   Construct this object with the then-branch functor template.

   Parameters: |
   `f` | Then-branch nullary functor template. The functor template call `f()` is actually compiled and executed for this template specialization (because the if-statement static predicate is `true`). The return type of `f()` must be the same as (or implicitly convertible to) the `ThenResult` type.

2.     operator ThenResult() const;

   This implicit type conversion returns a copy of the value returned by the call to the then-branch functor template.

3.     template<typename Else> ThenResult else_(Else const & f) const;

   Specify the else-branch functor template.

   Parameters: |
   `f` | Else-branch nullary functor template. The functor template call `f()` is never compiled or executed for this template specialization (because the if-statement static predicate is `true`). The return type of `f()` must be the same as (or implicitly convertible to) the `ThenResult` type.
   Returns: | A copy of the value returned by the call to the then-branch functor template (because the else-branch functor template call is not executed).

4.     template<bool ElseIfPred, typename ElseIfThen>
         call_if_statement< true, Then, ThenResult >
         else_if_c(ElseIfThen const & f) const;

   Specify an else-if-branch functor template (using a static boolean predicate).

   Parameters: |
   `f` | Else-if-branch nullary functor template. The functor template call `f()` is never compiled or executed for this template specialization (because the if-statement static predicate is `true`). The return type of `f()` must be the same as (or implicitly convertible to) the `ThenResult` type.
   Template Parameters: |
   `ElseIfPred` | Static boolean predicate selecting which functor template call to compile and execute.
   Returns: | A call-if statement so the else statement and additional else-if statements can be specified if needed. Eventually, it will be the return value of the then-branch functor template call for this template specialization (because the if-statement static predicate is `true`).

5.     template<typename ElseIfPred, typename ElseIfThen>
         call_if_statement< true, Then, ThenResult >
         else_if(ElseIfThen const & f) const;

   Specify an else-if-branch functor template (using a nullary boolean meta-function).

   Parameters: |
   `f` | Else-if-branch nullary functor template. The functor template call `f()` is never compiled or executed for this template specialization (because the if-statement static predicate is `true`). The return type of `f()` must be the same as (or implicitly convertible to) the `ThenResult` type.
   Template Parameters: |
   `ElseIfPred` | Nullary boolean meta-function selecting which functor template call to compile and execute.
   Returns: | A call-if statement so the else statement and additional else-if statements can be specified if needed. Eventually, it will be the return value of the then-branch functor template call for this template specialization (because the if-statement static predicate is `true`).