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PHP 7's new hashtable implementation

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Re: PHP 7's new hashtable implementation

#71

Post by gsg »

esailija wrote: post #65
skrebbel wrote: post #41

This is probably not a popular opinion, but I believe that PHP's associative array is one of the best-designed data structures in programming languages. Its main distinguishing property, as mentioned in this article, is that values can be indexed by key, but are still iterated in the order they were set. This is "do what I want" in so many cases that it's just nuts. Sure, just as often it's just needless overhead, bu…

JS objects don't have the same property, whatever order you see from iterating JS objects is only a side effect of the standard hidden class optimization, not because there was intention of having a certain order. In fact if you mix integer keys (which are represented differently) you will not get the "expected" iteration order: var o = { key: 3, 1: 4, value: 10, 0: 2 }; Object.keys(o) ["0", "1", "key", "value"] If i…

> only a side effect of the standard hidden class optimization, not because there was intention of having a certain order

Do you have a reference for this? I clearly recall a Lars Bak interview in which he says that adding a property .x and then .y results in an object of different hidden class than adding .y and then .x exactly because people want to rely on iteration order.

(Might not apply to numeric keys, though.)

Re: PHP 7's new hashtable implementation

#72

Post by nothrabannosir »

dsp1234 wrote: post #35
shimonamit wrote: post #29

Earlier quoted context omitted.

Javascript's arrays cannot be used as maps or associative arrays. Arrays require numeric, consecutive keys. Otherwise it's an Object. -- Clarification edit: Creating a new key on an array using arr['key']=1 creates a property on the arr Object but does not add an element to the standard array. http://stackoverflow.com/questions/8630471/strings-as-keys-o...

Adding non-numeric keys does not remove an Array's "arrayness" in JavaScript var x = []; console.log(Object.prototype.toString.call(x)); //[object Array] x[0] = 1; console.log(x[0]); //1 x["test"] = 2; console.log(x["test"]); //2 console.log(Object.prototype.toString.call(x)); //[object Array] x.map //function map() { [native code] } var y = {}; console.log(Object.prototype.toString.call(y)); //[object Object] y.map…

His point was:

    x = [1]; x["test"] = 555; x.map(function (y) { return y; });
    // [1]
That's [1], not [1, 555]. You can access the array from the map interface, but not the other way around.

Re: PHP 7's new hashtable implementation

#73

Post by mduerksen »

halflings wrote: post #45
skrebbel wrote: post #41

This is probably not a popular opinion, but I believe that PHP's associative array is one of the best-designed data structures in programming languages. Its main distinguishing property, as mentioned in this article, is that values can be indexed by key, but are still iterated in the order they were set. This is "do what I want" in so many cases that it's just nuts. Sure, just as often it's just needless overhead, bu…

> I hate that many other languages, including C#, Ruby and Python, force me to choose between either an unordered map or a list of (key, value) tuples Another commenter mentioned Python's OrderedDict, and Ruby's hashtables are ordered (from 1.9+): https://www.igvita.com/2009/02/04/ruby-19-internals-ordered-... It looks like C# also has an OrderedDictionary class: http://msdn.microsoft.com/en-us/library/system.collect…

Thanks for the pointers!

I find myself needing this surprisingly often:

An array of elements in a certain order which I also want to lookup by Id.

Sometimes the order is defined by configuration, sometimes by some other criteria that is not accessible for this particular component, so I can't resort to a SortedHashMap.

Still, I need a 1) fast and 2) convenient way of lookup by some key. Convenience is often more important to me than performance in those cases, since the data size is not huge, but I hate it when I have to write array.find(e => e.Key == myKey) instead of orderedLookup[myKey].

Re: PHP 7's new hashtable implementation

#74

Post by RossM »

skrebbel wrote: post #41

This is probably not a popular opinion, but I believe that PHP's associative array is one of the best-designed data structures in programming languages. Its main distinguishing property, as mentioned in this article, is that values can be indexed by key, but are still iterated in the order they were set. This is "do what I want" in so many cases that it's just nuts. Sure, just as often it's just needless overhead, bu…

I've found one use-case for mixed-keys: parsing complex headers. For example:

    Link: ; rel=stylesheet; type=text/css

    [
      [0] => 
      [rel] => stylesheet
      [type] => text/css
    ]
It doesn't come up very often.

Re: PHP 7's new hashtable implementation

#75

Post by [deleted] »

skrebbel wrote: post #41

This is probably not a popular opinion, but I believe that PHP's associative array is one of the best-designed data structures in programming languages. Its main distinguishing property, as mentioned in this article, is that values can be indexed by key, but are still iterated in the order they were set. This is "do what I want" in so many cases that it's just nuts. Sure, just as often it's just needless overhead, bu…

[deleted]

Re: PHP 7's new hashtable implementation

#76

Post by yedpodtrzitko »

pornel wrote: post #60
anonymoushn wrote: post #43

Earlier quoted context omitted.

Python has https://docs.python.org/2/library/collections.html#collectio... I've never wanted this though. I just discovered OrderedDict when I was looking for something like std::map.

> I've never wanted this though. When it's not the default normal thing, you don't build solutions around it, so you never see what you're missing :) In PHP I make lots of tiny uses of it in many places. I really missed it when I switched to Python (sure, there's OrderedDict, but it's a second-class citizen: there's no syntax for literals and standard APIs don't explicitly take advantage of it). * It's very useful fo…

What I read is "if all you have is a hammer, everything looks like a nail."

> In PHP I make lots of tiny uses of it in many places. I really missed it when I switched to Python (sure, there's OrderedDict, but it's a second-class citizen: there's no syntax for literals and standard APIs don't explicitly take advantage of it).

Missing syntax sugar makes it a second-class citizien? How? Also what advantages could standard API (> It's neat for sorting objects without having to mutate them to add a key or wrap them in a key/value object.

It's called set()

> It's great for configuration with JSON-like structures, but key order gives extra flexibility in the design, e.g. instead of [{id:"foo"},{id:"bar"}] you can use ["foo"=>[],"bar"=>[]].

...and the reason you cant use OrderedDict here is you dont like it.

About ordering stuff: after years I can still remember the problems I had with ordering in PHP. There's more than a dozen of sorting methods, which is mess. No one can remember if they all behave the same way and what's the order of its parameters. In Python you've sorted() and that's it. You cant do any advanced stuff with these array, because sometime they act as lists and sometime they act as hashmaps. I'll take this example from "Fractal...": $first = array("foo" => 123, "bar" => 456); $second = array("foo" => 456, "bar" => 123); array_diff($first, $second);

Re: PHP 7's new hashtable implementation

#77

Post by esailija »

gsg wrote: post #71
esailija wrote: post #65

Earlier quoted context omitted.

JS objects don't have the same property, whatever order you see from iterating JS objects is only a side effect of the standard hidden class optimization, not because there was intention of having a certain order. In fact if you mix integer keys (which are represented differently) you will not get the "expected" iteration order: var o = { key: 3, 1: 4, value: 10, 0: 2 }; Object.keys(o) ["0", "1", "key", "value"] If i…

> only a side effect of the standard hidden class optimization, not because there was intention of having a certain order Do you have a reference for this? I clearly recall a Lars Bak interview in which he says that adding a property .x and then .y results in an object of different hidden class than adding .y and then .x exactly because people want to rely on iteration order. (Might not apply to numeric keys, though.…

It results in different hidden class because the whole point is to be able to reference named fields by fixed offsets from the object location in memory (same as for example reading struct fields in C). If the order changes, so will the offsets too, so same names with different order must have different hidden classes.

Integer keys are not practical to treat as fixed because they are used as array indices 99% of the time which are dynamic. So they should be optimized differently, and they are. They are backed by a dynamically resized array (so it's implemented like Java's ArrayList). And it's not possible to track insertion order in this representation, so integer keys have different iteration order from named keys.

Note that doing hash-tabley things with the objects (like changing their property order constantly, deleting named keys and so on) will change the backing representation to ordered hash table. The ordered hash table emulates the same order that results from the nature of the above optimizations to make it less surprising for user when the representation changes. If it wasn't ordered, it would be very surprising when the iteration order suddenly changed from ascending integer keys and insertion ordered named keys to something completely random.

Re: PHP 7's new hashtable implementation

#78

Post by [deleted] »

skrebbel wrote: post #41

This is probably not a popular opinion, but I believe that PHP's associative array is one of the best-designed data structures in programming languages. Its main distinguishing property, as mentioned in this article, is that values can be indexed by key, but are still iterated in the order they were set. This is "do what I want" in so many cases that it's just nuts. Sure, just as often it's just needless overhead, bu…

[deleted]

Re: PHP 7's new hashtable implementation

#79

Post by Rapzid »

skrebbel wrote: post #41

This is probably not a popular opinion, but I believe that PHP's associative array is one of the best-designed data structures in programming languages. Its main distinguishing property, as mentioned in this article, is that values can be indexed by key, but are still iterated in the order they were set. This is "do what I want" in so many cases that it's just nuts. Sure, just as often it's just needless overhead, bu…

.Net has OrderedDictionary as well now.

Re: PHP 7's new hashtable implementation

#80

Post by debacle »

fleetfox wrote: post #55
cranklin wrote: post #46

Earlier quoted context omitted.

Those aren't primitive types

What are those called then? Wikipedia definition of primitive type is pretty vague. I don't think collections/containers can't be called primitive.

Collections are generally not primitives unless they are implemented in the language as primitives.
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