Lets say I have a GLib.Array<Item?> and want to convert that into a Item[], how would I do that in Vala?
First off, unless you need to for interoperability with existing code, don't use GLib.Array. Use GLib.GenericArray, which is much easier to use correctly and harder to use incorrectly.
GLib.Array.data is a regular array (Item?[] in your case), as is GLib.GenericArray.data, so you can just use that. If you assign it to an owned variable Vala will make a copy.
A naive approach would be, that you take out all the items from the array with the index() method and append them to an empty Item[] array, using +=.
A simple example program:
public int main (string[] args) {
Array<string> array = new Array<string> ();
array.append_val ("1. entry");
array.append_val ("2. entry");
string[] builtin = {};
for (var i = 0; i < array.length; i++) {
builtin += array.index (i);
}
return 0;
}
update: GLib.GenericArray really seems like a better solution. As for the data attribute: At GenericArray it is documented at Valadoc, at Array it isn't (that doesn't mean it does not work, but I haven't tried it).
Related
According to the documentation, it needs to follows the Form Post rules at: https://www.w3.org/TR/REC-html40/interact/forms.html#h-17.13.4. When looking at that information it did not give me much to work with in terms of complex objects or maps.
Right now, If I have a list for example: Each item in the list needs to be stringified.
var params = {"list": [1,2,3]};
// needs to be stringed.
params["list"] = params["list"].map((item)=>item.toString()).toList();
Simple. Also all base items need to be a string as well
var params = {"number": 1, "boolean": true};
params = params.forEach((k,v)=> params[k].toString());
But how do we handle maps?
var params = {"map": {"a":1,"b":"foo","c":false,"d":[]}};
// ??
It seems that after testing in my app and in dart pad, you need to make sure everything is strings, so i am trying to come up with a way to effectively cover lists, maps, and maybe more complex objects for encoding.
var params = {};
params["list"] = [1,2,3];
params["number"] = 1;
params["boolean"] = true;
params["map"] = {"a":1,"b":"foo","c":false,"d":[]};
params.forEach((String key, dynamic value){
if(value is List){
params[key] = value.map((v)=>v.toString()).toList();
}else if(value is Map){
// ????
}else{
params[key] = value.toString();
}
//maybe have an additional one for custom classes, but if they are being passed around they should already have their own JSON Parsing implementations.
}
Ideally, the result of this would be passed into:
Uri myUri = new Uri(queryParameters: params);
and right now, while i solved the list issue, it doesn't like receiving maps. Part of me just wanted to stringify the map as a whole, but i wasn't not sure if there was a better way. I know that when someone accidentally stringified the array, it was not giving me: ?id=1&id=2 but instead ?id=%5B1%2C2%5D which was not correct.
I don't think there is any special support for maps. Query parameters itself is a map from string to string or string to list-of-strings.
Everything else need to be brought into this format first before you can pass it as query parameter.
A simple approach would be to JSON encode the map and pass the resulting string as a single query parameter.
I'm building a FF extension, and I'm processing some xhtml for myself in order to supporn subforms loading, so I have to identify the elements with l10n attributes defined and add them the string value. Because the l10n can't be shared from main code to content scripts (because isn't a simple JSON object), I managed the situation by getting the loaded keys values and defining an "localized array bundle", like this:
lStrings = ["step_title", ........ ];
for (var i = 0; i < lStrings.length; i++) {
bundle[lStrings[i]] = this.locale(lStrings[i]);
}
The thing is, I have to write here every entry in the .properties files... SO, do you know how to access this key values? I already tryed with .toString .toLocalString and inspecting the object, but can't find the way the object to be capable of returning all the key collection.
Do you have a better idea for improvement?
var yourStringBundle = Services.strings.createBundle('chrome://blah#jetpack/content/bootstrap.properties?' + Math.random()); /* Randomize URI to work around bug 719376 */
var props = yourStringBundle.getSimpleEnumeration();
// MDN says getSimpleEnumeration returns nsIPropertyElement // https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XPCOM/Reference/Interface/nsIStringBundle#getSimpleEnumeration%28%29
while (props.hasMoreElements()) {
var prop = props.getNext();
// doing console.log(prop) says its an XPCWrappedObject but we see QueryInterface (QI), so let's try QI'ing to nsiPropertyElement
var propEl = prop.QueryInterface(Ci.nsIPropertyElement);
// doing console.log(propEl) shows the object has some fields that interest us
var key = propEl.key;
var str = propEl.value;
console.info(key, str); // there you go
}
See comments for learning. Nice quesiton. I learned more about QI from replying.
Given a Map, assignment, what is the fastest way to check if it contains any duplicate values in Dart? I am currently using a Set formed from the Map's values and checking its length against the original Map, which works of course, but I'm wondering if there's an especially performant alternative.
Set d = new Set.from(assignment.values);
if (d.length < assignment.length) {
return false; // indicates has duplicates in this context
}
EDIT:
Tried #mezoni's solution modified for my program, but it actually ran a bit slower than my original version. It probably has more to do with constant times than anything else.
List values = new List.from(assignment.values);
Set set = new Set();
for (var i = 0; i < assignment.length; i++) {
if (!set.add(values[i])) {
return false;
}
}
Complexity wise you won't be able to get anything faster. Creating the Set and filling it with the values of the Map is linear in the number of elements. Clearly you have to run through all the values, so you can't do any better than that.
Maybe you could find a solution with a smaller constant factor, but that's not clear. In particular for larger sets I think the Set solution is pretty efficient.
This is more of a algorithms question than a Dart question. In any case, you have to check every value against the others, giving n-1 + n-2 + ... + n-(n-1) checks, or n^2/2. Programmatically, it's easy to create a set, but you could also generate an array, sort the array, and then iterate once to check for duplicates. That finishes in O(n log n).
Fastets way (if you realy need better performance):
void main() {
// Values from map
var values = [1,2,3,2,1,3,2,1];
var length = values.length;
var set = new Set();
var duplicate = false;
// Only for statistics purpose
var statistics = 0;
for(var i = 0; i < length; i++) {
statistics++;
if(!set.add(values[i])) {
duplicate = true;
break;
}
}
print("Duplicate: $duplicate");
print("Performed in ${statistics} iteration(s) from $length possible");
}
Output:
Duplicate: true
Performed in 4 iteration(s) from 8 possible
P.S.
The first example can be recommended to use with List values.
But because Map.values not a List but Iterable then it would be more efficient do not convert them to List but use as is.
Here is modified sample for use with Iterable objects.
It will be work faster because in this algorithm not required convert all values to the List object because it not want using of all elements without exception.
Instead it wants use as less as possible access operation on original source. If the source supports lazy operation of the access to values (as Iterable) this will be even better.
void main() {
// Values from map
var values = [1,2,3,2,1,3,2,1];
var assignment = {};
var length = values.length;
var key = 0;
for(var value in values) {
assignment[key++] = value;
}
var set = new Set();
var duplicate = false;
// Only for statistics purpose
var statistics = 0;
for(var value in assignment.values) {
statistics++;
if(!set.add(value)) {
duplicate = true;
break;
}
}
print("Duplicate: $duplicate");
print("Performed in ${statistics} iteration(s) from $length possible");
}
function encodeBmp(s:String){
s = Base64.Encode(s);
var width:Number = Math.ceil(Math.sqrt(s.length/4));
var bmp:BitmapData = new BitmapData(width,width,true,0x00000000);
var pos:Number=0; //track position in string
for(var x:Number=0;x<width;x++){
for(var y:Number=0;y<width;y++){
var col="0x";
for(var i:Number=0;i<4;i++){
col+=getHex(s.charAt(pos));
pos++;
}
bmp.setPixel32(x,y,col);
trace(col + " > 0x" + bmp.getPixel32(x,y).toString(16));
}
}
return bmp.clone();
}
Basically, the trace statement returns this:
0x56326868 > 0x56326868
0x64434270 > 0x64424270
0x63794230 > 0x63794331
...
Why is the result of getPixel32 different from that of the set value, and how can I resolve this?
EDIT: getPixel is accurate, but doesn't have the extra bit that get/setPixel32 does... I would prefer to have more data per pixel.
You're Base64 encoding a String to store it in a BitmapData. I hope you didn't know that, or are ashamed.
Anyway, here is what I see happening:
First, if you type col as a String, you'll get a compile error on setPixel32, because it's expecting a uint.
Now, we can ignore all the looping and hex strings to get some simple code to reproduce the problem.
var bitmapData:BitmapData = new BitmapData(1, 1);
bitmapData.setPixel32(0, 0, 1682129520);
trace(bitmapData.getPixel32(0, 0));
By using an int literal, we can see that it's not a problem with type coercion, but something inside of BitmapData. This makes sense, since BitmapData is intended to store graphics data, so storing the graphics in a way that is graphically similar but not exact is fine.
You're probably seeing the side-effects of pre-multiplied alpha in Flash. This would also explain why you don't see any problems with getPixel and setPixel.
You can read more about it here: http://www.quasimondo.com/archives/000665.php
So how do you fix the problem? Use the correct data type. A ByteArray is designed to store binary data.
Does it imply that whenever I am passed an array of a non nullable type, I should still check if it is null? Actually it is not even possible to check <> null but have to use operator.unchecked .How is it better than C#?
type test=
{
value: int
}
let solution = Array.zeroCreate 10
solution.[0] <- {value = 1}
solution.[1].value // System.NullReferenceException: Object reference not set to an instance of an object
type test =
{value: int;}
val solution : test [] =
[|{value = 1;}; null; null; null; null; null; null; null; null; null|]
val it : unit = ()
It depends where the array is being passed from.
If the array is created and used only within F#, then no, you don't need to check for null; in fact, you shouldn't check for null (using Unchecked.defaultOf) because the F# compiler optimizes some special values like [] (and None, in certain cases) by representing them as null in the compiled IL.
If you're consuming an array being passed in by code written in another language (such as C#), then yes, you should still check for null. If the calling code just creates the array and doesn't mutate it any further, then you'll only need to perform the null checks once.
EDIT : Here's a previous discussion about how the F# compiler optimizes the representation of certain values using null: Why is None represented as null?
As the documentation for Array.zeroCreate indicates, it initializes the elements to Unchecked.defaultof<_>. This therefore carries with it all of the same caveats that direct use of Unchecked.defaultof does. Generally, my advice would be to use Array.create/Array.init whenever possible, and to treat Array.zeroCreate as a possible performance optimization (requiring care whenever dealing with non-nullable types).
You're creating a record type, which is implemented as a class, which is indeed nullable. If you intended to create a struct, your code should look something like this:
type test =
struct
val value: int
new(v) = { value = v }
override x.ToString() = x.value.ToString()
end
let solution = Array.zeroCreate 10
solution.[0] <- test(1)
This outputs: val solution : test [] = [|1; 0; 0; 0; 0; 0; 0; 0; 0; 0|]
You could also write the type using the Struct attribute, saving you a level of indentation.
[<Struct>]
type test =
val value: int
new(v) = { value = v }
override x.ToString() = x.value.ToString()