2.2 Argument Deduction

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When we call a function template such as max() for some arguments, the template parameters are determined by the arguments we pass. If we pass two int s to the parameter types T const& , the C++ compiler must conclude that T must be int . Note that no automatic type conversion is allowed here. Each T must match exactly. For example:

 template <typename T>  inline T const& max (T const& a, T const& b);   max(4,7)  // OK:  T  is  int  for both arguments  max(4,4.2)  // ERROR: first  T  is  int  , second  T  is  double 

There are three ways to handle such an error:

1. Cast the arguments so that they both match:

    max(static_cast<double>(4),4.2)  // OK  

2. Specify (or qualify) explicitly the type of T:

    max<double>(4,4.2)  // OK  

3. Specify that the parameters may have different types.

For a detailed discussion of these topics, see the next section.

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