Question

I have to check hashrefs like this one

{ foo => 65, bar => 20, baz => 15 }

against an arrayref of hashrefs expressing conditions like this

[
 { foo => { "<=" => 75 } },
 { bar => { "==" => 20 } },
 { baz => { ">=" => 5 } },
]

and return a true value if all conditions are fulfilled.

Neither of the two data structures is pre-determined. One is built from parsing a string in a database, the other from parsing user input.

In the case above, I would return true, but if I checked the hashref against

[
 { foo => { "<=" => 60 } },
 { bar => { "==" => 20 } },
 { baz => { ">=" => 5 } },
]

I would return false, because foo in the first hashref is not <= 60.

The question is: what’s the best strategy for doing that?

I am thinking of

• building a series of subrefs via eval
• checking against the appropriate one among 5 different pre-built subrefs (one per case for >, <, <=, >= and ==)

Am I going down the wrong path altogether? and if not, what’s the best, eval or pre-built functions?

I have looked into Params::Validate but I am concerned that it’d be a lot of overhead, and I’d have to build the callbacks anyway.

Answer 1

Use code references instead, and you will have ready to go validators. I simplified your condition-structure. There is no need to have an extra array level in there, unless you have duplicate hash keys, which I assume you don’t.

The simplistic sub { $_[0] <= 75 } will simply compare the first value of the arguments. By default, the last value evaluated in the subroutine will be its return value.

use v5.10;
use strict;
use warnings;

my $in = { foo => 65, bar => 21, baz => 15 };

my $ref = {
    foo => sub { $_[0] <= 75 } ,
    bar => sub { $_[0] == 20 } ,
    baz => sub { $_[0] >= 5 } ,
};

for my $key (keys %$in) {
    if ($ref->{$key}($in->{$key})) {
        say "$key : Valid";
    } else {
        say "$key : Invalid";
    }
}

Output:

bar : Invalid
baz : Valid
foo : Valid