On 2019-12-04 00:40, ToddAndMargo via perl6-users wrote:
Hi All,
I am cooking up something where I want top pass a value to a sub, but I
want to restrict what those values are.
For instance, things like
AbortRetryIgnore
CancelRetryContinue
Help
YesNo
Maybe
And so on and so forth.
If the wrong value is passed, I want the checker to crash
the sub.
What is the best way of going about this?
Many thanks,
-T
Follow up:
This may be a duplicate. But I can't find it in my sent bin,
so I am re-sending my keeper on what I came up with that
I like.
Perl6: constraining variable in sub declarations:
References:
https://stackoverflow.com/questions/59222421/perl6-raku-how-to-i-restrict-the-values-allowed-in-a-variable
https://docs.raku.org/type/Signature#index-entry-where_clause
Note: the `where clause` not confined to just subs.
Example format:
sub foo( Int $binary where * ~~ 0|1 ) { ... }
Sample sub:
sub abc( Str $x where * ~~ "abc" | "def" ) {say $x;}
abc("abc")
abc
abc("def")
def
abc("hij")
Constraint type check failed in binding to parameter '$x';
expected anonymous constraint to be met but got Str ("hij")
