Check if coercion would be successful?

Question

Given

my $t=+"aaa";

is it possible tho check if the coercion will succeed (I know that it doesn't here) before using $t ?

BTW: What I really want to do is check if a string is a valid Integer. I know that I can use a regex for that purpose, but I suppose that there is a simpler solution.

Answer 1

+'aaa' results in a Failure which is a kind of Nil which is a bit like an undefined value. Which means you can use anything that works with them.

my $t = +$s with +$s; # $t remains undefined

my $t = +$s // 0; # $t === 0

my $t = (+$s).defined ?? +$s !! 0;

Since what you want to do is check if it is an Int

my $t = +$s ~~ Int ?? +$s !! 0; # Failures aren't a type of Int

my $t = 0;
with +$s {
  when Int { $t = $_ }
  default { ... } # +$s is defined
} else {
  ... # optional else clause
}

Answer 2

Yet another version:

my $t = +"aaa" orelse note "could not coerce to numeric type";
say $t.^name; # Failure

orelse is the low-precedence version of //. In this version, the assignment to $t still happens, but the check for definedness handles the failure, ie it won't blow up and raise an error.