Chapter 3 Templates

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Chapter 3 Templates

• Saurav Karmakar
• Spring 2007

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Objective

• In Chapter 3, we will discuss
• The concept of a template
• Function templates
• Class templates
• vector and matrix classes

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3.1 What is a Template

• A mechanism for writing routines that work for
  arbitrary types w/o knowing these types (type
  independent).
• Most likely be seen in generic algorithm
  implementations, i.e. find max, swapping, sorting
  searching.

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3.2 Function Templates

• typedef keyword for defining new type from an
  existing one.Ex
• typedef double Object
• void swap( Object lhs, Object rhs)
• Object temp lhs
• lhs rhs
• rhs temp

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3.2 Function Templates

• A function template is not an actual function,
  instead its a design or a pattern, for what
  could become an actual function.
• A function template is a design or pattern for a
  function which allows processors to generate an
  actual function from this design.

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Function template example Swap routine

• typedef double Object
• void swap(Object lhs,
• Object rhs)
• Object tmp lhs
• lhs rhs
• rhs tmp
• // figure 3.1
• Note swap is part of the STL

• template ltclass Objectgt
• void swap(Object lhs,
• Object rhs)
• Object tmp lhs
• lhs rhs
• rhs tmp
• // figure 3.2

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Swap routine used in main function

• int main()
• int x 5, y 7
• double a 2, b 4
• swap (x,y) // swap(int,int)
• swap(x,y) //reuse previous instantiation
• swap(a,b) //swap(double, double)
• //swap(x, b) // illegal no match
• return 0
• // figure 3.3

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3.3 A Sorting Function Template

• template ltclass Comparablegt
• void insertionSort(vectorltComparablegt a)
• for(int p 1 p lt a.size() p)
• Comparable tmp ap
• int j
• for(j p j gt 0 tmp lt aj-1 j--)
• aj a j 1
• aj tmp

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Insertion Sort example

• The given insertionSort routine work for double,
  int, float but not char, (primitive string),
  because operator and lt are undefined.

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3.4 Class Templates

• A class can be a template.
• Example vector is a class template
•  C Class Templates are used where we have
  multiple copies of code for different data types
  with the same logic.
• If a set of functions or classes have the same
  functionality for different data types, they
  becomes good candidates for being written as
  Templates.
• When possible, constant reference should be used
  instead of call by value because if object is a
  large object, making a copy could be inefficient.
  (or illegal if copy constructor is disable or not
  defined)

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A class template example

• template ltclass Objectgt
• class MemoryCell
• public
• explicit MemoryCell(const Object initVal
  Object())
• storedValue(initVal)
• const Object read() const
• return storedValue
• void write(const Object x)
• storedValue x
• private
• Object storedValue
• // figure 3.8

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Typical template interface

• templateltclass objectgt
• class ClassName
• public
• //public members
• private
• //private member

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Typical member implementation

• template ltclass objectgt
• ReturnType
• ClassNameltobjectgtmemberName(parameterList)
  /const/
• // member body

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Interface of the template

• templateltclass Objectgt
• class MemoryCell
• public
• explicit MemoryCell(const Object
  initVal Object())
• const Object read() const
• const write(const Object x)
• private
• Object storedValue
• // figure 3.10

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Summary

• Discussion of template facilities
• Template for generic algorithms