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Multiple return values

Some ACSUtils functions return multiple values (e.g. 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.

Here's an example, RotateVector returns X and Y:

RotateVector(x, y, angle);
int newX = r1;
int newY = r2;
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:

int b = r2;

Because SomeOtherFunction may call functions that overwrite r2! Instead, strictly follow this style:

int a = r1;
int b = r2;

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.
ParseFixed("1.0", 10);
int error = r1;
int result = r2; // no compiler error, despite assigning a fixed to int

But overwriting argument variables immediately after calling the function is valid:

RotateVector(x, y, angle);
x = r1;
y = r2;

An example of a function returning three values:

normalize3d(x, y, z);
int newX = r1;
int newY = r2;
int newZ = r3;
multiple_return_values.txt · Last modified: 2019/04/22 00:32 by korshun