One should ask the question what happens if the list runs out of values in the middle, of a multi-value iteration? That is, what happens to the follow loop?
tutorial/arrays/missing_values.p6
#!/usr/bin/env perl6
use v6;
for (1, 2, 3, 4, 5) -> $x, $y {
say "$x $y";
}
say 'done';
In this case Rakudo throws an exception when it finds out it does not have enough values for the last iteration. It will look like this, (with a bunch of trace information afterwards).
tutorial/arrays/missing_values.p6.output
1 2 3 4 Not enough positional parameters passed; got 1 but expected 2 in block <anon> at examples/arrays/missing_values.p6:4
In order to avoid the exception we could tell the loop that the second and subsequent values are optional by adding a question mark after the variable
tutorial/arrays/missing_values_fixed.p6
#!/usr/bin/env perl6
use v6;
for (1, 2, 3, 4, 5) -> $x, $y? {
say "$x $y";
}
say 'done';
This will work but generate the following output:
tutorial/arrays/missing_values_fixed.p6.output
1 2 3 4 use of uninitialized value of type Mu in string context in block <anon> at examples/arrays/missing_values_fixed.p6:5 5 done
Published on 2012-01-01