Changes between Initial Version and Version 1 of RefactoringSteps/ExtractFunction

Timestamp:

Feb 18, 2012, 4:43:19 PM (13 years ago)

Author:

manualwiki

Comment:

--

RefactoringSteps/ExtractFunction

@@ +1 @@
+= Extract function =
+
+A function definition might contain an expression or a sequence of expressions which can be considered as a logical unit, hence a function definition can be created from it. The extracted function is lifted to the module level, and it is parameterized with the free variables of the original expressions: those variables which are bound outside of the expressions, but the value of which is used by the expressions.
+
+Extracting the new function {{{two_sol}}}:
+
+{{{
+-module(quadratic).
+
+-export([f/0]).
+
+solve(A,B,C) ->
+   D := B * B - 4 * A * C,
+   if
+      D == 0 ->
+         {-B / 2 / A};
+      D > 0 ->
+         S = math:sqrt(D),
+         {-(B+S)/2/A,
+         -(B-S)/2/A}.
+      D < 0 ->
+         no_solution
+   end.
+}}}
+
+Result:
+
+{{{
+-module(quadratic).
+
+-export([f/0]).
+
+solve(A,B,C) ->
+   D := B * B - 4 * A * C,
+   if
+      D == 0 ->
+         {-B / 2 / A};
+      D > 0 ->
+         two_sol(A, B, D);
+      D < 0 ->
+         no_solution
+   end.
+
+two_sol(A, B, D) ->
+   Sqrt = math:sqrt(D),
+   {-(B+S)/2/A,
+    -(B-S)/2/A}.
+}}}
+
+== Side conditions ==
+
+ * The name of the new function should not conflict with another function, either defined in the same module, or imported from another module (overloading). Furthermore, the name should be a legal function name.
+ 
+ * If one of the above conditions fails, the transformation starts an interaction to ask for a new function name.
+
+ * The starting and ending positions should delimit a sequence of expressions.
+
+ * Variables with possible binding occurrences in the selected sequence of expressions should not appear outside of the sequence of expressions.
+
+ * The extracted sequence of expressions cannot be part of a guard sequence.
+
+ * The extracted sequence of expressions cannot be part of a pattern.
+
+ * The extracted sequence of expressions cannot be part of macro definition.
+
+
+== Transformation steps and compensations ==
+
+ 1. Collect all variables that the selected sequence of expressions depends on.
+
+ 2. Collect variables from the selected variables in step 1, which has binding occurrence out of the selected part of the module.
+
+ 3. Add a new function definition to the current module with a single alternative. The name of the function is an argument to the refactoring. The formal parameter list consists of the variables selected in step 2.
+
+ 4. Replace the selected sequence of expressions with a function call expression, where the name of the function is given as an argument to the refactoring, and the actual parameter list consists of the variables selected in step 2.
+
+ 5. The order of the variables must be the same in steps 3 and 4.
+
+ 6. If the selected expression is a block-expression, eliminate the begin-end keywords from the expression in the body of the created new function.