Do not repeat yourself, we teach every fledgling software developer. It makes sense as with growing code redundancy the maintenance cost increase. Simple tools such as functions or loops are a great ways to reduce code redundancy but in our quest to avoid code redundancy we sometimes indulge into complexity. Complex code is also costly to maintain. I will demonstrate, using real-world examples, how one can adopt metaprogramming to minimize code redundancy as well keeping the code simple enough for my mom to understand it.

1. Pragmatic MetaProgramming
Mårten Rånge
SWETUGG 10:50

2. Mårten Rånge
@marten_range

3. Pragmatic MetaProgramming

4. DNRY
Do Not Repeat Yourself

5. Loops are great
x += 1;
x += 2;
x += 3;
x += 4;
x += 5;
x += 6;
x += 7;
x += 8;
x += 9;
x += 10;

6. Loops are great
for (var iter = 1; iter < 11; ++iter)
{
x += iter;
}

7. Functions are great
var z1 = t*(y1 – x1) + x1
var z2 = t*(y2 – x2) + x2
var z3 = t*(y3 – x3) + x3

8. Functions are great
double Lerp (this double t, double x, double y)
{
return t*(y – x) + x;
}
var z1 = t.Lerp (x1, y1);
var z2 = t.Lerp (x2, y2);
var z3 = t.Lerp (x3, y3);

9. Repeating myself
[Serializable]
public class AnException : Exception
{
public AnException ();
public AnException (string message);
public AnException (string message, Exception exc);
protected AnException (
SerializationInfo info, StreamingContext context);
[SecurityPermission(
SecurityAction.Demand, SerializationFormatter = true)]
public override void GetObjectData (
SerializationInfo info, StreamingContext context)
}

10. Repeating myself
AnException Exception

11. Repeating myself
[Serializable]
public class AnException : Exception
{
public AnException ();
public AnException (string message);
public AnException (string message, Exception exc);
protected AnException (
SerializationInfo info, StreamingContext context);
[SecurityPermission(
SecurityAction.Demand, SerializationFormatter = true)]
public override void GetObjectData (
SerializationInfo info, StreamingContext context)
}

12. Repeating myself
exception AnException of int*string

13. Repeating myself
public class MyViewModel : INotifyPropertyChanged
{
int m_myProperty = 0;
public int MyProperty
{
get { return m_myProperty; }
set
{
m_myProperty = value
OnRaisePropertyChanged ("MyProperty")
}
}
void OnRaisePropertyChanged (string propertyName);
}

14. Repeating myself
int MyProperty

15. Repeating myself
public class MyViewModel : INotifyPropertyChanged
{
int m_myProperty = 0;
public int MyProperty
{
get { return m_myProperty; }
set
{
m_myProperty = value
OnRaisePropertyChanged ("MyProperty")
}
}
void OnRaisePropertyChanged (string propertyName);
}

16. Repeating myself
class Customer
{
public long Id ;
public string FirstName;
public string LastName ;
}
public Customer ReadCustomer (IDataReader dr)
{
return new Customer
{
Id = dr.GetInt64 (0),
FirstName = dr.GetString (1),
LastName = dr.GetString (2),
};
}

17. Repeating myself
class Customer
{
public long Id ;
public string FirstName;
public string LastName ;
}
public Customer ReadCustomer (IDataReader dr)
{
return new Customer
{
Id = dr.GetInt64 (0),
FirstName = dr.GetString (1),
LastName = dr.GetString (2),
};
}

18. Repeating myself
Customer
long Id
string FirstName
string LastName

19. Repeating myself
class Customer
{
public long Id ;
public string FirstName;
public string LastName ;
}
public Customer ReadCustomer (IDataReader dr)
{
return new Customer
{
Id = dr.GetInt64 (0),
FirstName = dr.GetString (1),
LastName = dr.GetString (2),
};
}

20. Code duplication increases maintenance cost

21. Looking for answers
 Reflection
 LINQ Expression Trees
 Dynamic IL

22. Adding complexity
 Trading compile-time errors for run-time errors
 Hard to get enough test coverage
 Hard to understand
 No exit strategy
 Risky to change
 Limited

24. public Customer ReadCustomer (IDataReader dr)
{
return new Customer
{
Id = dr.GetInt64 (0),
FirstName = dr.GetString (1),
LastName = dr.GetString (2),
};
}

25. Adding complexity
 Trading compile-time errors for run-time errors
 Hard to get enough test coverage
 Hard to understand
 No exit strategy
 Risky to change
 Limited

26. Complex code increases maintenance cost

29. Looking for answers
Powerful
Simple concept
Language agnostic
Exit strategy
Lightweight

30. T4

31. class Example
{
public int X0 = 0;
public int X1 = 1;
public int X2 = 2;
public int X3 = 3;
public int X4 = 4;
public int X5 = 5;
public int X6 = 6;
public int X7 = 7;
public int X8 = 8;
public int X9 = 9;
}
T4

32. class Example
{
<# for (var iter = 0; iter < 10; ++iter) { #>
public int X<#=iter#> = <#=iter#>;
<# } #>
}
T4

33. class Example
{
public int X0 = 0;
public int X1 = 1;
public int X2 = 2;
public int X3 = 3;
public int X4 = 4;
public int X5 = 5;
public int X6 = 6;
public int X7 = 7;
public int X8 = 8;
public int X9 = 9;
}
T4

34. Demo.001
Getting started with T4

35. Betty Holberton
Merge Sort Generator (1951)

36. Repeating myself
public class MyViewModel : INotifyPropertyChanged
{
int m_myProperty = 0;
public int MyProperty
{
get { return m_myProperty; }
set
{
m_myProperty = value
OnRaisePropertyChanged ("MyProperty")
}
}
void OnRaisePropertyChanged (string propertyName);
}

37. Repeating myself
public class MyViewModel : INotifyPropertyChanged
{
int m_myProperty = 0;
public int MyProperty
{
get { return m_myProperty; }
set
{
m_myProperty = value
OnRaisePropertyChanged ()
}
}
void OnRaisePropertyChanged ([CallerMemberName]string name = null);
}

38. Repeating myself
int MyProperty

39. Repeating myself
public class MyViewModel : INotifyPropertyChanged
{
int m_myProperty = 0;
public int MyProperty
{
get { return m_myProperty; }
set
{
m_myProperty = value
OnRaisePropertyChanged ("MyProperty")
}
}
void OnRaisePropertyChanged (string propertyName);
}

40. Demo.002
Generating view model classes

41. T4
Powerful
Simple concept
Language agnostic
Exit strategy
Lightweight

42. Carnelian

43. class Example
{
<# for (var iter = 0; iter < 10; ++iter) { #>
public int X<#=iter#> = <#=iter#>;
<# } #>
}
T4

44. class Example
{
@@> for iter in 0..10
public int X@@=iter=@@ = @@=iter=@@;
@@> end
}
Carnelian

45. Demo.003
Carnelian

46. Carnelian
Powerful
Simple concept
Language agnostic
Exit strategy
Lightweight

47. Start small

48. class Example
{
<# for (var iter = 0; iter < 10; ++iter) { #>
public int X<#=iter#> = <#=iter#>;
<# } #>
}
T4 is ASP/PHP for code

49. T4 saved me

50. Mårten Rånge
@marten_range

51. T4
T4 Addin
http://t4-editor.tangible-engineering.com/
T4 Blog
http://www.olegsych.com/
T4Include
http://github.com/mrange/t4Include/

52. ”The CORRECT Way to Code a Custom Exception Class”
http://bit.ly/1AsJ0UH

53. Vad tyckte du om sessionen?
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