Re^2: storing and using LoL path

Sorry all, for not being too descriptive.. The closest I want to accomplish is the this example u shown :

my %map = (
    typeA => sub { $_[0]->{key1}[3]{key2} },
    typeB => sub { $_[0]->{key3} },
    typeC => sub { $_[0]->[1]{key4} },
    # ...
);
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i.e. in my concentrate case I was looping over a result of SOAP::Lite. Which depending on the type of the object places the 'price' in different places f.e.

$$obj{cost}  <--type1
$$obj{priceList}{price}  <--type2
$$obj{priceList}{price}{value}  <--type3
...etc..
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So instead of doing alot of if-typeX, I thought it will be good if I can store the access-path in some way and do a simple hash lookup.
Is it more clear now ;)
(Something like XPath on LoL)

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Re^3: storing and using LoL path by almut (Canon) on May 26, 2007 at 02:03 UTC
The closest I want to accomplish is the this example u shown : `my %map = ( typeA => sub { $_[0]->{key1}[3]{key2} }, typeB => sub { $_[0]->{key3} }, typeC => sub { $_[0]->[1]{key4} }, # ... );` [download] In what way does this not do what you described? Well, another way would be to store the "XPath" as a string in the hash, and then `eval` it at runtime, i.e. `my %map = ( typeA => "{key1}[3]{key2}", typeB => "{key3}", typeC => "[1]{key4}", # ... ); for my $elem (@LoANY) { my $xpath = $map{$elem->{type}}; my $lol = $elem->{data}; print eval "\$lol->$xpath", "\n"; }` [download] With the example data from my previous post, this would also print `Value1 Value2 Value3` [download] In other words, you construct snippets of literal Perl source (e.g. `"\$lol->$xpath"`, interpolating to `'$lol->{key1}[3]{key2}'`), which you then `eval`. Thing is that the XPath thing would need to be turned into runnable code — either at compile-time (like in the function dispatcher approach shown first), or with an `eval` at runtime. Expect a performance penalty though, if you call the `eval` many many times... (Update: not to mention that using `eval` would require some awareness of security issues, if you apply it in scenarios where the code being constructed dynamically is potentially coming from insecure sources)	[reply] [d/l] [select]

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Re^3: storing and using LoL path
by almut (Canon) on May 26, 2007 at 02:03 UTC

The closest I want to accomplish is the this example u shown :

my %map = ( typeA => sub { $_[0]->{key1}[3]{key2} }, typeB => sub { $_[0]->{key3} }, typeC => sub { $_[0]->[1]{key4} }, # ... );
[download]

In what way does this not do what you described?

Well, another way would be to store the "XPath" as a string in the hash, and then eval it at runtime, i.e.

my %map = (
    typeA => "{key1}[3]{key2}",
    typeB => "{key3}",
    typeC => "[1]{key4}",
    # ...
);

for my $elem (@LoANY) {
    my $xpath = $map{$elem->{type}};
    my $lol   = $elem->{data};
    print eval "\$lol->$xpath", "\n";
}
[download]

With the example data from my previous post, this would also print

Value1
Value2
Value3
[download]

In other words, you construct snippets of literal Perl source (e.g. "\$lol->$xpath", interpolating to '$lol->{key1}[3]{key2}'), which you then eval. Thing is that the XPath thing would need to be turned into runnable code — either at compile-time (like in the function dispatcher approach shown first), or with an eval at runtime.

Expect a performance penalty though, if you call the eval many many times... (Update: not to mention that using eval would require some awareness of security issues, if you apply it in scenarios where the code being constructed dynamically is potentially coming from insecure sources)

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