This works ok:
//somewhere in Foo:
static function bar(arg:StringMap<Dynamic>) {trace(arg.toString())}
...
//somewhere in build macro:
var myArr = [macro "k1"=>100, macro "k2"=>200, macro "k3"=>300];
var newExpr = macro {
Foo.bar($a{myArr});
}
But in reality sometimes myArr.length == 0 and this gives compilation error:
Array<Unknown<0>> should be haxe.ds.StringMap<Dynamic>
So I should replace $a{myArr} with null or new StringMap() if the length of myArr is zero, but how can I do this?
Currently I did this:
var newExpr = myArr.length == 0 ?
macro {
Foo.bar(null);
} : macro {
Foo.bar($a{myArr});
};
But in reality the code in macro is bigger...
You can run conditionals inside your macro reification with ${}
var newExpr = macro Foo.bar(${myArr.length == 0 ? macro null : macro $a{myArr}});
The solution is very easy:
var myArr = [macro "k1"=>100, macro "k2"=>200, macro "k3"=>300];
...
var arrExpr = myArr.length == 0 ? macro new Map<String, Dynamic>() : macro $a {myArr};
var newExpr = macro {
Foo.bar($arrExpr);
}
Related
This is a question that aims merely at elegance, but is there a way to make something to the following code work in Swift? I know the code does not work, what I want is that the result of the code within the closure is stored in a constant. And the underlying theoretical issue is whether or not it is possible to retrieve the returned value from the closure with type Int and not with type () -> Int.
Thanks a lot for any help or comment!
let tableWithBooleans: [Bool] = Array(repeating: false, count: 10)
tableWithBooleans[0] = true
tableWithBooleans[5] = true
let numberOfTrue: Int = {
var result: Int = 0
for i in 0...9 {
if tableWithBooleans[i] {
result += 1
}
}
return result
}
// I want the code to compile and numberOfTrue to be a constant equal to 2
Use a high-order function instead
let numberOfTrue = tableWithBooleans.reduce(0) { $1 ? $0 + 1 : $0 }
Now if you still want to use your closure code then you should add a () after the closing } since you are calling the code inside {} as a function
let numberOfTrue: Int = {
var result: Int = 0
for i in 0...9 {
if tableWithBooleans[i] {
result += 1
}
}
return result
}()
I created a function that recieves input and compare it to a list, when find a match it return the match, in this case this match is the attribute of a class that i created.
I understand that the problem is with the return statement, so in the beginning of the function I declare the return as "Any", further more than that I'm kinda lost.
The error is this: A 'return' expression required in a function with a block body ('{...}')
class Class1(var self: String)
var test_class = Class1("")
fun giver(){
test_class.self = "Anything"
}
class Funciones(){
fun match_finder(texto: String): Any{
var lista = listOf<String>(test_class.self)
var lista_de_listas = listOf<String>("test_class.self")
var count = -1
for (i in lista_de_listas){
count = count + 1
if (texto == i){
lista_de_listas = lista
var variable = lista_de_listas[count]
return variable
}
}
}
}
fun main(){
giver()
var x = "test_class.self"
var funcion = Funciones()
var y = funcion.match_finder(x)
println(y)
}
To explain you what the problem is, let's consider the following code:
class MyClass {
fun doSomething(): String {
val numbers = listOf(1, 2, 3)
for (number in numbers) {
if (number % 2 == 0) {
return "There is at least one even number in the list"
}
}
}
}
If you try compiling it you'll get the same error message as in your question: A 'return' expression required in a function with a block body ('{...}'). Why is that?
Well, we defined a function doSomething returning a String (it could be any other type) but we're returning a result only if the list of numbers contains at least one even number. What should it return if there's no even number? The compiler doesn't know that (how could it know?), so it prompts us that message. We can fix the code by returning a value or by throwing an exception:
class MyClass {
fun doSomething(): String {
val numbers = listOf(1, 2, 3)
for (number in numbers) {
if (number % 2 == 0) {
return "There is at least one even number in the list"
}
}
// return something if the list doesn't contain any even number
return "There is no even number in the list"
}
}
The same logic applies to your original code: what should the function return if there is no i such that texto == i?
Please also note that the solution you proposed may be syntactically correct - meaning it compiles correctly - but will probably do something unexpected. The for loop is useless since the if/else statement will always cause the function to return during the first iteration, so the value "There is no match" could be returned even if a match actually exists later in the list.
I searched online, if someone has the same problem, the correct code is as follows:
class Funciones(){
fun match_finder(texto: String): Any{
var lista = listOf<String>(test_class.self)
var lista_de_listas = listOf<String>("test_class.self")
var count = -1
var variable = " "
for (i in lista_de_listas){
count = count + 1
if (texto == i){
lista_de_listas = lista
var variable = lista_de_listas[count]
return variable
} else {
return "There is no match"
}
}
return variable
}
}
I have an issue with my n variable. I cannot use n in for loop. Why? n was initialized before for loop. Please, help.
import Foundation
var n: Int
var t: Int
while(true){
var tt = readLine()
t = Int(tt!)!
if (t==0){
break
}
else if ( t < 0){
n = t*(-1)
}
else if(t > 0){
n = t
}
var arr : [[String]] = []
for i in 0..<n*2{
for y in 0..<n*2{
arr[i][y] = "."
}
}
}
A variable may be declared and not immediately initialized, as long as initialization is guaranteed before first use
The error is more subtle than at first glance. You may actually declare a property without initializing it, as long as all program flows leading to its first use ascertain initialization of it.
The issue is with the if, else if and else if block:
var n: Int // declaration
// ...
if (t == 0) {
break
}
else if (t < 0) {
n = t*(-1)
}
else if (t > 0){
n = t
}
// first use
for i in 0..<n*2 { /* ... */ }
Swift cannot not infer that this block is in fact exhaustive, and believes that there is a possibility that none of the above if statements holds, which, in the eyes of the compiler, would lead to the following program state:
program flow has not been broken (break)
and n has not been instantiated
As humans, however, we know that the if - else if - else if block above is indeed exhaustive, and can help the compiler out by simply changing the last if else statement to a simple else statement.
if (t == 0) {
break
}
else if (t < 0) {
n = t*(-1)
}
// if none of the above, t > 0
else {
n = t
}
On another note, the nested array access of non-existing array elements, arr[i][y] = "." will lead to a runtime exception, but this is another issue. In its current form, it looks as if the intent with the nested loops could be replaced with a nested array instantiation:
var arr = [[String]](repeating: [String](repeating: ".", count: 2*n), count: 2*n)
or,
var arr = (0..<2*n).map { _ in [String](repeating: ".", count: 2*n) }
The variable n is only declared, not initialized.
To initialize the variables:
var n: Int = 0
var t: Int = 0
I have the following code :
def generateStoriesnew(outputPath: String, groupedRDD:RDD[(String,Iterable[String])], isInChurnMode: Boolean, isInChurnPeriod: Boolean) {
val windowedRDD = groupedRDD.map(SOME CODE)
var windowedRDD2 = windowedRDD.filter(r => r != null).map(a=>a.churnPeriod(isInChurnPeriod,isInChurnMode))
val prettyStringRDD = windowedRDD2.map(r => {
r.toString
})
prettyStringRDD.saveAsTextFile(outputPath)
}
and here is the code for ChurnPriod function:
def churnPeriod( churnPeriod:Boolean, churnMode: Boolean): Unit = {
if (churnMode && rootEventType.equalsIgnoreCase("c")){
var churnCustStory: CustStoryN = null
var nonChurnCustStory: CustStoryN = null
var churnPeriodEventStory: mutable.MutableList[StoryEventN] = null
var NonChurnEventstory: mutable.MutableList[StoryEventN] = null
churnPeriodEventStory = new mutable.MutableList[StoryEventN]
NonChurnEventstory = new mutable.MutableList[StoryEventN]
var lastEventChurnPeriod = true
var currentEventStory = eventStory
var max = currentEventStory.length
println(max);
if (currentEventStory.size > 0) {
for (i <- 0 until currentEventStory.length) {
var currentEvent = currentEventStory(i)
if (currentEvent.timeSenseRootEvent < 90) {
churnPeriodEventStory.+=(currentEvent)
//lastEventChurnPeriod = true
}
else {
NonChurnEventstory.+=(currentEvent)
lastEventChurnPeriod = false
}
}
}
if (churnPeriod)
eventStory = churnPeriodEventStory
else
eventStory=null
}
}
but churn period function does not change eventstory which is a member of a custstory class. what am I missing here ?
class CustStoryN (val custId:String,
var rootEventType:String,
var rootEventTime:Long,
var eventStory:mutable.MutableList[StoryEventN])
my hypothesis is either:
1.map is not the right transformation for the function that I have
2.churnPeriod function never get called
3.I can not change eventstory which is a member of cust story class
Does anyone have any idea how I can troubleshoot this problem?
This would be trivial to determine by debugging. Just put a few breakpoints and you can see if the program stops inside the function, and what transformations do occur.
My guess would be that the problem is this line: if (currentEventStory.size > 0), thus, a list that starts at size 0 remains at size 0 forever. Another option is that churnPeriod is never true, thus, you compute a lot but never assign to the eventStory variable.
Your code does need a good cleanup ;-)
For the following code:
inc = -> value = (value ? 0) + 1
dec = -> value = (value ? 0) - 1
print = -> console.log value ? 0
How can you make this work properly, so inc and dec close upon value instead of creating separate function-local variables, in the way other than explicitly assigning something to value?
In plain Javascript, you would just declare var value at outer scope:
var value;
function inc() { value = (value || 0) + 1; };
function dec() { value = (value || 0) - 1; };
function print() { console.log(value || 0); };
What is CoffeeScript way for exactly the same thing?
In CoffeeScript, the way to introduce a local variable is to assign to the variable in the appropriate scope.
This is simply the way that CoffeeScript was defined and as such is similar to Python or Ruby, which do not require a "variable declaration", except CoffeeScript also allows forward access. A side-effect is that one cannot shadow a lexical variable.
Just as with the placement of var in JavaScript, where this assignment is done (as long as it is in the correct scope) does not affect the scope of the variable.
Given
x = undefined
f = -> x
// JS
var f, x;
x = void 0;
f = function() {
return x;
};
Given
f = -> x
x = undefined
// JS
var f, x;
f = function() {
return x;
};
x = void 0;