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multiple_return_values [2019/04/19 21:13] – korshunmultiple_return_values [2019/04/22 00:32] (current) – korshun
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-====== Multiple return values convention ======+====== Multiple return values ======
  
-Some ACSUtils functions return multiple values (e.g. [[math#vector_math|vector math functions]]). ACS doesn't support returning multiple values from a function.+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.
  
 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. 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.
  
-Here's an example:+Here's an example, ''RotateVector'' returns X and Y:
  
 <code> <code>
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 </code> </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:
 +<code>
 +SomeFunctionWithMultipleReturnValues(...);
 +SomeOtherFunction(r1);
 +int b = r2;
 +</code>
 +Because ''SomeOtherFunction'' may call functions that **overwrite ''r2''**! Instead, strictly follow this style:
  
 +<code>
 +SomeFunctionWithMultipleReturnValues(...);
 +int a = r1;
 +int b = r2;
  
 +SomeOtherFunction(a);
 +</code>
 +</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.1555697598.txt.gz · Last modified: 2019/04/19 21:13 by korshun

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