Transformation Priority Premise
Introduction to TPP
If we go back to how we evolve code in TDD, we have these methods:
Introduction to classic TDD“Use obvious implementation” is ambiguous, what does “obvious implementation” mean? It may mean something for you and something else for another developer. The transformations on the following table are a way to clarify ambiguity the “obvious implementation”.
#
Transformation
Start code
End code
1
{} -> nil
{}
[return] nil
2
Nil -> constant
[return] nil
[return] “1”
3
Constant -> constant+
[return] “1”
[return] “1” + “2”
4
Constant -> scalar
[return] “1” + “2”
[return] argument
5
Statement -> statements
[return] argument
[return] min(max(0, argument), 10)
6
Unconditional -> conditional
[return] argument
if(condition) [return] argument else [return] 0
7
Scalar -> array
dog
[dog, cat]
8
Array -> container
[dog, cat]
{dog=”DOG”, cat=”CAT”}
9
Statement -> tail recursion
a + b
a + recursion
10
If -> loop
if(condition)
loop(condition)
11
Statement -> recursion
a + recursion
recursion
12
Expression -> function
today – birth
CalculateBirthDate()
13
Variable -> mutation
day
var Day = 10; Day = 11;
14
Case/Switch
Transformations on the top of the list should be preferred to those that are lower. It is better (or simpler) to change a constant into a variable than it is to add an if statement. So when making a test pass, you try to do so with transformations that are simpler (higher on the list) than those that are more complex. Please do not take this table literally. This is a starting point. Adapt this table to your language and environment.
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