Re: Re: Recursion, tree parsing.

You can probably get away without checking for the existance of @{$t->{children}}.

Eh, yer probably right.

But why would I want to do:

change:

if(@{$t->{children}}){

with

if($#{$t->{children}} > 0){
[download]

Comment on Re: Re: Recursion, tree parsing. Select or Download Code

Replies are listed 'Best First'.
Re: Re: Re: Recursion, tree parsing. by demerphq (Chancellor) on Apr 15, 2003 at 07:38 UTC
why would I want to do You wouldn't. :-) I _think_ the issue the OP was refering to (but actually doesnt deal with) is the possibility that children is undef. Since the dereference is a fetch it wont be automagically created and the `if ( @{...} )` will choke. Personally I would replace it and the for with the following `for my $child ( @{ $t->{children} \|\| [] } ) { }` [download] Normally I dont put so much whitespace in my expressions, but I figured here it makes things clearer, When dereferencing, if $t->{children} is false then we use an empty anonymous array to iterate over. We dont have to check if there are elements, because if there are, we _will_ iterate over them, and if there are, well, we _wont_. BTW, Its a good idea to become quite familiar with binary trees before you play with n-ary trees. It helps to solidy the concepts. A good learning exercise is to implement a Tie::Hash using a binary tree. (Say a sorted hash implemented using a binary tree?) Incidentally any tree structure can be represented using binary trees if necessary so it pays off to understand them well. HTH --- demerphq _{<Elian> And I do take a kind of perverse pleasure in having an OO assembly language...}	[reply] [d/l] [select]

Replies are listed 'Best First'.

Re: Re: Re: Recursion, tree parsing.
by demerphq (Chancellor) on Apr 15, 2003 at 07:38 UTC

why would I want to do

You wouldn't. :-) I _think_ the issue the OP was refering to (but actually doesnt deal with) is the possibility that children is undef. Since the dereference is a fetch it wont be automagically created and the if ( @{...} ) will choke. Personally I would replace it and the for with the following

for my $child ( @{ $t->{children} || [] } ) {
}
[download]

Normally I dont put so much whitespace in my expressions, but I figured here it makes things clearer, When dereferencing, if $t->{children} is false then we use an empty anonymous array to iterate over. We dont have to check if there are elements, because if there are, we _will_ iterate over them, and if there are, well, we _wont_.

BTW, Its a good idea to become quite familiar with binary trees before you play with n-ary trees. It helps to solidy the concepts. A good learning exercise is to implement a Tie::Hash using a binary tree. (Say a sorted hash implemented using a binary tree?) Incidentally any tree structure can be represented using binary trees if necessary so it pays off to understand them well.

HTH

_{<Elian> And I do take a kind of perverse pleasure in having an OO assembly language...}

[reply]
[d/l]
[select]