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0 pointsamirkdv5y ago0 comments

I'm not the original comment author, neither am I fluent in Perl. But I suspect they meant nested hashes and not a hash whose values are arrays of arrays. As you point out, the latter is trivial.

To be clear, even a nested hash is all well as long as the depth and the keys are literals (as in your example). It is when keys are dynamic that things get unruly. And god forbid if the _depth_ of nesting is dynamic. All of these are trivial to implement in Python, Ruby, JS, PHP, ...

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gbacon5y ago

    %nested = (foo => { bar => { baz => "quux" } });

Access the leaf with

    $nested->{foo}{bar}{baz}

If the keys are in variables, it becomes

    $nested->{$x}{$y}{$z}

For dynamic depth, do you have a specific use case in mind? If I have a tree, I’m probably going to search it rather than using a hardcoded path.

kbenson5y ago

This is why we use strict! The extra arrow is unneeded, as you're working on the actual hash, not a reference to the hash. This is a compiler error with use strict though, so it's not something you would generally be bitten with when writing real code, just internet comments. :)

gbacon5y ago

Whoops, good catch! I had references on the brain. For completeness, that makes it either

    $nested{$x}{$y}{$z}

or after initializing with curly brackets rather than parentheses to construct a new reference to an anonymous hash

    $nested = { … };

and then use the arrow to dereference as in the grandparent.

cookiecaper5y ago

I think the point is not that Perl's rules don't make sense -- it's that they're much less obvious than those in many competing languages. In Python, lists are `l = [1, 2, 3]` and dicts are `d = {"key": val}`. Both structures can be nested without any change to the semantics.

j / k navigate · click thread line to collapse

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gbacon5y ago

    %nested = (foo => { bar => { baz => "quux" } });

Access the leaf with

    $nested->{foo}{bar}{baz}

If the keys are in variables, it becomes

    $nested->{$x}{$y}{$z}

For dynamic depth, do you have a specific use case in mind? If I have a tree, I’m probably going to search it rather than using a hardcoded path.

kbenson5y ago

gbacon5y ago

Whoops, good catch! I had references on the brain. For completeness, that makes it either

    $nested{$x}{$y}{$z}

or after initializing with curly brackets rather than parentheses to construct a new reference to an anonymous hash

    $nested = { … };

and then use the arrow to dereference as in the grandparent.

cookiecaper5y ago

j / k navigate · click thread line to collapse