For some reason, one of my JS files is triggering an unsafe-eval Content Security Policy violation on my site. I thought this odd because there is no eval() anywhere in the file. The error happens on the following line:
setTimeout(callSpecific(), (lengthMF * (number.length + 2)));
The only thing I can see here is the arithmetic on the RHS that sets the timeout value. So, I tried:
setTimeout(callSpecific(), (parseInt(lengthMF) * (parseInt(number.length) + 2)));
Same thing. The variables themselves are not even strings - they are defined as:
var lengthMF = 150;
var number = ""; // yes, this is a string but number.length is not!
Why is this triggering a CSP violation? I have other setTimeout()s on the page and this seems to be the only problematic one. The weird thing is replacing the arithmetic expression temporarily with a constant (e.g. 50) does not cause the issue to go away.
If it's necessary, callSpecific() looks something like this:
function callSpecific() {
if (number == 0) {
operatorRing();
} else if (number.length == 2 && number.charAt(1) == 0) {
playReorder();
} else if (number.length == 3) {
//
} else if (number.length <7 || number.length > 11) {
//
} else if (number.length == 11 && (number.charAt(4) == 1 || number.charAt(4) == 0)) {
//
}
}
Related
This amounts to testing for xor (one or the other but not both and not neither) where the task demands something is done for the one but not for the other but we abandon the project if both or neither.
This example might be most to the point but the empty block doesn't sit well with me
if (condition == 1) {
do something
}
elsif (condition == 2) {
; # do nothing aka carry on
}
else {
exit;
}
Nesting seems no better and in this example misses (ie, does not validate) the second condition
if (condition) {
if (condition == 1) {
do something
}
}
else {
exit;
}
Combining both of the above avoids the empty block and will work but forces redundant testing and seems inefficient.
if ((condition == 1) || (condition == 2)) {
if (condition == 1) {
do something
}
}
else {
exit;
}
Is there an alternative I haven't thought of? Why might one choose one structure over another? Thanks for your insights.
if (condition == 1) {
do something
}
elsif (condition == 2) {
; # do nothing aka carry on
}
else {
exit;
}
and
if ((condition == 1) || (condition == 2)) {
if (condition == 1) {
do something
}
}
else {
exit;
}
are equivalent to
if (condition == 1) {
do something
}
elsif (condition != 2) {
exit;
}
None of the above test for "one or the other but not both and not neither". For that, you'd need the following:
if (condition == 1 || condition == 2) {
do something
}
Since condition can't be both 1 and 2, no further checks are needed. On the other hand, if you had two independent conditions, you could literally use xor.
if (condition1 xor condition2) {
do something
}
Warning: This is a low-precedence operator (like not, and and or), so you may need to put parens around both of the expressions it has for operands.
my %dispatch = {
1 => sub { dosomething() },
2 => sub { dosomethingelse() },
}
exists $dispatch{$condition} ?
$dispatch{$condition}->() :
do_default();
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 am downgrading Swift code from Xcode 8.3.1 to Xcode 7.3.1.
The Swift compiler of Xcode 7.3.1 raises
Expression was too complex to be solved in reasonable time; consider breaking up the expression into distinct sub-expressions
while pointing on line zeroParameterAndPaths.sort {. The code was ok in Xcode 8.3.1.
What's wrong and how to fix it?
class NewConnectingSegmentZeroParameterAndPath {
let step : Int; // 0 = main, 1 = first outline, 2 = second outline
let parameter : CGFloat;
init(step: Int, parameter: CGFloat) {
self.step = step;
self.parameter = parameter;
}
}
var zeroParameterAndPaths : [NewConnectingSegmentZeroParameterAndPath] = [];
// ... some zeroParameterAndPaths .appendContentsOf calls
zeroParameterAndPaths.sort {
return $0.parameter < $1.parameter
|| ($0.parameter == $1.parameter
&& ($0.step == 1 || ($0.step == 0 && $1.step == 2))
)
};
You have two choices. One is simply to do what the error message suggests, i.e. pulling the complex bool apart into separate pieces:
zeroParameterAndPaths.sort {
let bless = ($0.parameter < $1.parameter)
let beq = ($0.parameter == $1.parameter)
let band = ($0.step == 0 && $1.step == 2)
let bor = ($0.step == 1 || band)
let beqandbor = (beq && bor)
return (bless || beqandbor)
};
The other is to provide an explicit in line giving the param types and result type:
zeroParameterAndPaths.sort {
(a:NewConnectingSegmentZeroParameterAndPath, b:NewConnectingSegmentZeroParameterAndPath) -> Bool in
return a.parameter < b.parameter
|| (a.parameter == b.parameter
&& (a.step == 1 || (a.step == 0 && b.step == 2))
)
};
You could also make your class a little bit more helpful and make it implement the condition. The compiler is much less likely to get confused in a function body than in a closure:
class NewConnectingSegmentZeroParameterAndPath {
let step : Int; // 0 = main, 1 = first outline, 2 = second outline
let parameter : CGFloat;
init(step: Int, parameter: CGFloat) {
self.step = step;
self.parameter = parameter;
}
func orderedBefore(_ other: NewConnectingSegmentZeroParameterAndPath) -> Bool
{
return parameter < other.parameter
|| parameter == other.parameter
&& (step == 1 || step == 0 && other.step == 2)
}
}
var zeroParameterAndPaths : [NewConnectingSegmentZeroParameterAndPath] = [];
// ... some zeroParameterAndPaths .appendContentsOf calls
zeroParameterAndPaths.sort { $0.orderedBefore($1) }
Apart from the issue of the type inference engine not being able to quickly resolve such complex bool expressions, such expressions are really hard to follow. I suggest you break it down into something simpler, like so:
zeroParameterAndPaths.sort {
if $0.parameter != $1.parameter { return $0.parameter < $1.parameter ]
if $0.step == 1 { return true }
if $0.step == 0 && $1.step == 2 { return true }
return false
};
There's my attempt at it. I'm not even sure if it's correct, the original expression is pretty hard to follow.
I'm currently converting C++ code to Swift and I've gotten stuck on one part. The parameter passed into the function is a string and the area where I'm stuck is when attempting to set a variable based on the second to last character of a string to check for a certain character.
The error shows up on this line:
line[i-1]
I've tried casting this value to an Int but this didn't work:
Int(line[i - 1])
I've also tried to see if the string's startIndex function which takes a Int would work but it didn't:
line.startIndex[i - 1]
Here is the full function:
func scanStringForSpecificCharacters(line: String){
var maxOpen: Int = 0;
var minOpen: Int = 0;
minOpen = 0;
maxOpen = 0;
var i = 0
while i < line.characters.count {
for character in line.characters {
//var c: Character = line[i];
if character == "(" {
maxOpen += 1;
if i == 0 || line[i - 1] != ":" {
minOpen += 1;
}
}
else if character == ")"{
minOpen = max(0,minOpen-1);
if i == 0 || line[i-1] != ":"{
maxOpen -= 1;
}
if maxOpen < 0{
break;
}
}
}
if maxOpen >= 0 && minOpen == 0{
print("YES")
}else{
print("NO")
}
}
}
Strings in Swift aren't indexed collections and instead you can access one of four different views: characters, UTF8, UTF16, or unicodescalars.
This is because Swift supports unicode, where an individual characters may actually be composed of multiple unicode scalars.
Here's a post that really helped me wrap my head around this: https://oleb.net/blog/2016/08/swift-3-strings/
Anyway, to answer you question you'll need to create an index using index(after:), index(before:), or index(_, offsetBy:).
In your case you'd want to do something like this:
line.index(line.endIndex, offsetBy: -2) // second to last character
Also, you'll probably find it easier to iterate directly using a String.Index type rather than Int:
let line = "hello"
var i = line.startIndex
while i < line.endIndex {
print(line[i])
i = line.index(after: i)
}
// prints ->
// h
// e
// l
// l
// o
Working with Strings in Swift was changed several times during it's evolution and it doesn't look like C++ at all. You cannot subscript string to obtain individual characters, you should use index class for that. I recommend you read this article:
https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/StringsAndCharacters.html
As already pointed out in the other answers, the compiler error
is caused by the problem that you cannot index a Swift String with
integers.
Another problem in your code is that you have a nested loop which is
probably not intended.
Actually I would try to avoid string indexing at all and only
enumerate the characters, if possible. In your case, you can
easily keep track of the preceding character in a separate variable:
var lastChar: Character = " " // Anything except ":"
for char in line.characters {
if char == "(" {
maxOpen += 1;
if lastChar != ":" {
minOpen += 1;
}
}
// ...
lastChar = char
}
Or, since you only need to know if the preceding character is
a colon:
var lastIsColon = false
for char in string.characters {
if char == "(" {
maxOpen += 1;
if !lastIsColon {
minOpen += 1;
}
}
// ...
lastIsColon = char == ":"
}
Another possible approach is to iterate over the string and a shifted
view of the string in parallel:
for (lastChar, char) in zip([" ".characters, line.characters].joined(), line.characters) {
// ...
}
As others have already explained, trying to index into Swift strings is a pain.
As a minimal change to your code, I would recommend that you just create an array of the characters in your line up front:
let linechars = Array(line.characters)
And then anywhere you need to index into the line, use linechars:
This:
if i == 0 || line[i-1] != ":" {
becomes:
if i == 0 || linechars[i-1] != ":" {
This is my original function in Swift 2:
// check on winning combinations
func checkWinnerMove(){
for var i = 0; i<winningCombinations.count && !isWinner;i += 1 {
if gameState[winningCombinations[i][0]-1] == activePlayer &&
gameState[winningCombinations[i][1]-1] == activePlayer &&
gameState[winningCombinations[i][2]-1] == activePlayer{
isWinner = true;
}else{
isWinner = false;
}
}
}
I have changed it to this:
// check on winning combinations
func checkWinnerMove(){
for i in 0 ..< winningCombinations.count && !isWinner{
if gameState[winningCombinations[i][0]-1] == activePlayer &&
gameState[winningCombinations[i][1]-1] == activePlayer &&
gameState[winningCombinations[i][2]-1] == activePlayer{
isWinner = true;
}else{
isWinner = false;
}
}
}
But keep getting a error when I add the
&& !isWinner
statment in the for-in loop. The error I get is:
No '..<' candidates produce the expected contextual result type 'Bool'
Any suggestions? Thank You!
Instead of forcibly trying to rewrite your original C-style for loop, consider what you're trying to achieve and attempt to re-write it in "native" Swift from scratch. How about breaking out of your loop once your true condition is met, instead of keeping it in the loop signature? E.g.
for i in 1...5 {
print(i)
if i == 3 { break }
} // 1 2 3
Applied to your example
func checkWinnerMove()
isWinner = false
for i in 0 ..< winningCombinations.count {
if gameState[winningCombinations[i][0]-1] == activePlayer &&
gameState[winningCombinations[i][1]-1] == activePlayer &&
gameState[winningCombinations[i][2]-1] == activePlayer {
isWinner = true
break
}
}
}
The explicit by index access of the (unknown for us) gameState and winningCombinations sequences is quite "unswifty" w.r.t. in the dangers of runtime exceptions for indices out of range for the sequences. So bear in mind that there are safer ways to perform such access.
For future reference, consider reading How to create a Minimal, Complete, and Verifiable example: since we (the potential answerer's of your question) don't have access to/the full information regarding isWinner, winningCombinations, gameState or activePlayer, we can't verify your example. Also, since the question cover a concept, it could be boiled down to a more minimal form. (Welcome to StackOverflow!)