New to the Svelte community and try to understand the framework (compiler?).
So I tried the following code:
App.svelte:
<script>
let count = 1;
$: {
console.log(`Before A: ${count}`);
count = 2;
console.log(`A: ${count}`);
}
$: {
console.log(`B: ${count}`);
}
$: {
console.log(`Before C: ${count}`);
count = 3;
console.log(`C: ${count}`);
}
$: {
console.log(`D: ${count}`);
}
</script>
A running prototype can be found here.
Please check find the output of the code from console.
Output:
"Before A: 1"
"A: 2"
"Before C: 2"
"C: 3"
"B: 3"
"D: 3"
It seems that the reactive statements including assignment of reactive value have been hoisted.
Is there any references about that behavior and explain why?
Quote the answer by fs99 from discord:
so basically all reactive statements run top-to-bottom, unless they depend on other reactive statements running first. In this case, A and C modify count, so A runs first, then C, then the others: again top-to-bottom, B and D.
Related
In the context of Jenkins pipelines, I have some Groovy code that's enumerating a list, creating closures, and then using that value in the closure as a key to lookup another value in a map. This appears to be rife with some sort of anomaly or race condition almost every time.
This is a simplification of the code:
def tasks = [:]
for (platformName in platforms) {
// ...
tasks[platformName] = {
def componentUploadPath = componentUploadPaths[platformName]
echo "Uploading for platform [${platformName}] to [${componentUploadPath}]."
// ...
}
tasks.failFast = true
parallel(tasks)
platforms has two values. I will usually see two iterations and two tasks registered and the keys in tasks will be correct, but the echo statement inside the closure indicates that we're just running one of the platforms twice:
14:20:02 [platform2] Uploading for platform [platform1] to [some_path/platform1].
14:20:02 [platform1] Uploading for platform [platform1] to [some_path/platform1].
It's ridiculous.
What do I need to add or do differently?
It's the same issue as you'd see in Javascript.
When you generate the closures in a for loop, they are bound to a variable, not the value of the variable.
When the loop exits, and the closures are run, they will all be using the same value...that is -- the last value in the for loop before it exited
For example, you'd expect the following to print 1 2 3 4, but it doesn't
def closures = []
for (i in 1..4) {
closures << { -> println i }
}
closures.each { it() }
It prints 4 4 4 4
To fix this, you need to do one of two things... First, you could capture the value in a locally scoped variable, then close over this variable:
for (i in 1..4) {
def n = i
closures << { -> println n }
}
The second thing you could do is use groovy's each or collect as each time they are called, the variable is a different instance, so it works again:
(1..4).each { i ->
closures << { -> println i }
}
For your case, you can loop over platforms and collect into a map at the same time by using collectEntries:
def tasks = platforms.collectEntries { platformName ->
[
platformName,
{ ->
def componentUploadPath = componentUploadPaths[platformName]
echo "Uploading for platform [${platformName}] to [${componentUploadPath}]."
}
]
}
Hope this helps!
According to the documentation, the function identical checks whether two references are to the same object.
With that in mind, I don't understand why the following is the case:
int a = 1;
int b = 1;
print(identical(a, b)); // prints 'true'
Map c = { 1: 'y' };
Map d = { 1: 'y' };
print(identical(c, d)); // prints 'false'
I'd expect both calls to return 'false'.
identical compares references. a and b are references to a compile time literal 1. Thus they are identical.
I'm trying to draw some boxes in Rascal and trying to give each box its own callback function. On entering the box with the mouse the corresponding string should get displayed in the text element (so hovering box1 should display box1 etc.).
However, at the moment the text does pop up but just displays "box3" for each of the 3 boxes.
Any ideas?
strings = ["box1", "box2", "box3"];
boxes = [ box(
size(100, 100),
onMouseEnter(void() {
output = s;
})
) | s <- strings];
render(hcat([
vcat(boxes),
text(str () {return output;})
]));
Good question, classical problem. The essence of the problem is that Rascal uses "non-capturing closures": this means that functions that are returned from another function share the same context. In your case this is the variable s introduced by s <- strings. This nearly always happens when you create function values in a loop (as you do here). The solution is to wrap another function layer around the returned function.
Here is a simple example:
list[int()] makeClosures()
= [ int() {return i;} | i <- [0,1,2]];
void wrong(){
lst = makeClosures();
println(lst[0]());
println(lst[1]());
println(lst[2]());
}
which will print surprisingly the values 2,2and2`. The solution is, as said, to introduce another function level:
int() makeClosure(int i)
= int() { return i;};
list[int()] makeClosuresOK()
= [ makeClosure(i) | i <- [0,1,2]];
void right(){
lst = makeClosuresOK();
println(lst[0]());
println(lst[1]());
println(lst[2]());
}
now calling right() will print 1, 2, and 3 as expected.
I leave it as an exercise how this is done in your example, but I am prepared to give a solution when you ask for it. Good luck!
I have a variable in groovy like below:
project.Map
{
time.'1 1 * ?' = ['T1']
time.'2 1 * ?' = ['T2']
templates.'T1' = ['Z','X','Y']
templates.'T2' = ['Q']
}
Sorry but I am new to groovy ,when i try to access the individual
variable values in project.map how do i access them
i tried something like below
log.info(grailsApplication.config.project.Map.time[1])
log.info(grailsApplication.config.project.Map.get('time.'2 1 * ?'' ))
log.info(grailsApplication.config.project.Map.get('time[0]' ))
log.info(grailsApplication.config.project.Map.time.get('1 1 * ?'))
but they all print null value or object references.how do i access values for
time and templates both within a for loop and without it.
please see http://grails.org/doc/latest/guide/conf.html#config for the ways the config is allowed to nest. your outer syntax is especially mentioned to not be allowed:
However, you can't nest after using the dot notation. In other words, this won't work:
// Won't work!
foo.bar {
hello = "world"
good = "bye"
}
You have to write it as
project { Map { ... } }
The inner dotted parts (with the assignment) are ok (according to the doc)
Just wondering what's the meaning of ":" (colon symbol) on this Javascript code below?
var switchToTarget : Transform;
Thanks,
Gino
Edit: Reading more about Unity, they have created a really custom implementation of JavaScript(1) for their scripting engine, which is compiled and it has a lot of strongly typing features, it looks like ActionScript/ES4, but it isn't, the language is called UnityScript.
The colon is used by this implementation to denote the type of an identifier, e.g.:
class Person{
var name : String;
function Person(n : String){
name = n;
}
function kiss(p : Person){
Debug.Log(name + " kissed " + p.name + "!");
}
}
See also:
UnityScript Reference
Head First into Unity with JavaScript
Scripting Overview
Unity Answers
The code you posted is not valid ECMAScript 3, (which is the most widely implemented standard), that will simply give you a SyntaxError.
The colon symbol in JavaScript has only a few usages:
The object literal syntax:
var obj = { foo: 'bar' };
The conditional operator:
var test = condition ? 'foo' : 'bar';
Labeled statements:
loop1: while (true) {
while (true) {
break loop1; // stop outer loop
}
}
Case and default clauses of the switch statement:
switch (value) {
case "foo":
//..
break;
default:
//..
break;
}
It can appear on RegExp literals:
var re = /(?:)/; // non-capturing group...
It's Adobe ActionScript, which is a derivative of javascript.
var switchToTarget : Transform; // declare var switchToTarget of type Transform.
var hello : Text = new Text(); // declare var hello of type Text and initialize it.
http://www.adobe.com/livedocs/flash/9.0/ActionScriptLangRefV3/flash/geom/Transform.html
I'm not sure if it's part of standard JavaScript, but it declares the type of a variable.
var myVar:Type;
in that flavor of JavaScript would be equivalent to this in several strongly-typed languages:
Type myVar;