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DADiSP Developer's Guide > Chapter 2: SPL > Optional Function Arguments
A function argument is optional if it is not referenced when the function is invoked.
func1(x, y)
{
if (x < 0)
return(y);
else
return(x);
}
func1(1) returns: 1
func1(-1) returns: y: Unknown Variable
Optional arguments can be tested using the argc variable:
optfun(a, b)
{
/* default b and/or a if not specified */
if (argc < 2)
{
if (argc < 1) a = 1;
b = 10;
}
return(a * b);
}
optfun(2, 3) returns: 6
optfun(2) returns: 20
optfun() returns: 10
Arguments can also be assigned default values directly in the argument list:
optfun2(a = 1, b = 10)
{
return(a * b);
}
optfun2(2, 3) returns: 6
optfun2(2) returns: 20
optfun2() returns: 10
The default value of an argument can be any valid value. Default values can depend on arguments that occur earlier in the argument list.
optfun3(a = 10, b = 1..3, c = a * b)
{
return(a + b + c);
}
optfun3() returns: {21, 32, 43}
optfun3(1) returns: {3, 5, 7}
optfun3(1, 2) returns: 5
Specifying default argument values in the SPL argument list can greatly simplify the initialization steps of an SPL function.
The outargc variable indicates how many variables will be assigned by a function. For example:
outtest(x)
{
if (outargc > 1)
{
return(x, x * x);
}
else
{
return(x);
}
}
a = outtest(1..100)
(a, b) = outtest(1..100)
In both assignments, a is set to the series 1..100, however in the first example, the squared series x*x is not calculated since outargc is 1.
outargc allows multi-value functions to be more efficient by testing whether a particular return value even needs to be calculated.