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multiple_return_values [2017/03/21 14:35] – korshunmultiple_return_values [2019/04/19 22:41] – korshun
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-====== Multiple return values ======+====== Multiple return values convention ======
  
-ACSUtils uses a simple convention for functions returning multiple values, like [[functions:RotateVector]]:+Some ACSUtils functions return multiple values (e.g. [[math#vector_math|vector math functions]], but also some non-math functions). ACS doesn't support returning multiple values from a function.
  
-There are global variables r1 through r8. The functions write their return values to them.+ACSUtils uses a convention to fake returning multiple values from a function. The convention is as follows: there are 8 global variables with names ''r1'' through ''r8''. If a function returns multiple values, it actually returns no value and writes the first "returned" value to ''r1'', the second one to ''r2'', and so on.
  
-    RotateVector(x, y, angle); // Call the function +Here's an example, ''RotateVector'' returns X and Y:
-    int newX = r1; // Get the first returned value +
-    int newY = r2; // And the second one+
  
-<note warning>You should retrieve the return values **as soon as possible**, or else they may get overwritten by other functions that return multiple values.+<code> 
 +RotateVector(x, y, angle); 
 +int newX = r1; 
 +int newY = r2; 
 +</code> 
 + 
 +<note warning> 
 +You should retrieve the return values **as soon as possible**, or else they may get overwritten by other functions that return multiple values.
  
 Don't do this: Don't do this:
 <code> <code>
-SomeFunctionWithMultipleReturns(...);+SomeFunctionWithMultipleReturnValues(...);
 SomeOtherFunction(r1); SomeOtherFunction(r1);
 int b = r2; int b = r2;
 </code> </code>
-Because SomeOtherFunction may call functions that **overwrite r2**!!! +Because ''SomeOtherFunction'' may call functions that **overwrite ''r2''**! Instead, strictly follow this style:
- +
-Instead, strictly follow this style:+
  
 <code> <code>
-SomeFunctionWithMultipleReturns(...);+SomeFunctionWithMultipleReturnValues(...);
 int a = r1; int a = r1;
 int b = r2; int b = r2;
Line 29: Line 32:
 </code> </code>
 </note> </note>
 +
 +<note important>Another shortcoming is that ''r1''..''r8'' are declared ''raw'' in BCC to be able to accomodate any type of return value, and thus bypass [[strict typing]], even if it's enabled.
 +
 +<code>
 +ParseFixed("1.0", 10);
 +int error = r1;
 +int result = r2; // no compiler error, despite assigning a fixed to int
 +</code>
 +
 +</note>
 +
 +But overwriting argument variables immediately after calling the function is valid:
 +<code>
 +RotateVector(x, y, angle);
 +x = r1;
 +y = r2;
 +</code>
 +
 +An example of a function returning three values:
 +<code>
 +normalize3d(x, y, z);
 +int newX = r1;
 +int newY = r2;
 +int newZ = r3;
 +</code>
  
multiple_return_values.txt · Last modified: 2019/04/22 00:32 by korshun

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