I am trying to generate an automatic password code, however, I get an error with the below code "Cannot convert value of type '[Any]' to specified type 'String'
Output of debugger as follows:
expression failed to parse:
error: Loops + Function.playground:7:25: error: cannot convert value of type '[Any]' to specified type 'String'
var passString:String = []
^~
warning: Loops + Function.playground:9:5: warning: immutable value 'n' was never used; consider replacing with '_' or removing it
for n in 0...5 {
^
_
let alphabet = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"]
var passString:String = []
for n in 0...5 {
passString = passString + alphabet.randomElement()!
}
print(passString)
Related
I'm new to Swift and is trying to learn the concept of optional binding. I have came up with the following code:
let possibleNumber = Int("123")
possibleNumber.dynamicType
if let actualNumber = Int(possibleNumber){
print("\(possibleNumber) has an integer value of \(actualNumber)")
} else {
print("\(possibleNumber) could not be converted to an int")
}
Xcode playground output error message:
value of optional type "int?" not unwrapped, did you mean to use "!" or "?"
However, when I added the "!" to if let actualNumber = Int(possibleNumber!){
let possibleNumber = Int("123")
possibleNumber.dynamicType
if let actualNumber = Int(possibleNumber!){
print("\(possibleNumber) has an integer value of \(actualNumber)")
} else {
print("\(possibleNumber) could not be converted to an int")
}
Xcode display another error message:
initialiser for conditional binding must have Optional type, not int
Why is this happening?
The result of
let possibleNumber = Int("123")
is an optional Int - Int?
Then you're trying to create another Int with
Int(possibleNumber)
which does not work because the initializer expects a non-optional type.
The error message is related to the initializer rather than to the optional binding.
Try this to get the same error message.
let possibleNumber = Int("123")
let x = Int(possibleNumber)
In your second example when you initialize an Int with an implicit unwrapped Int! argument you get a non-optional Int and the compiler complains about the missing optional.
In the if let construct
if let actualNumber = Int(possibleNumber!){
print("\(possibleNumber) has an integer value of \(actualNumber)")
}
you don't need to use the Int initializer. You simply need to write
if let actualNumber = possibleNumber {
print("\(possibleNumber) has an integer value of \(actualNumber)")
}
Now Swift will try to unwrap possibleNumber. If the operation does succeed the unwrapped value is put inside actualNumber and the THEN block executed.
In pre-Swift 2.0 sample code, I've come across something like:
var val = "hello" + Repeat(count: paddingAmount, repeatedValue: "-") + "."
In Xcode 7.0/Swift 2.0 Playground, this produces the error:
note: expected an argument list of type '(String, String)'
How would you use the Repeat collection and get the value that's held by the collection for use?
String has an initializer that will return a string of repeated characters, I would recommend using that in your case:
let padding = String(count: paddingAmount, repeatedValue: Character("-"))
var val = "hello" + padding + "."
It's now Array(count: paddingAmount, repeatedValue: "-").
if (RARRAY_LEN(arr) > 0)
{
VALUE str = rb_ary_entry(arr, 0);
abc = some_method(*str);
}
rb_ary_entry(arr, 0) gives me an index value. Then I want to convert that value to a string so I can pass it to the next method. I tried:
rb_str_new2(rb_ary_entry(arr, 0));
but I get error saying:
error: indirection requires pointer operand `('VALUE' (aka 'unsigned long')` `invalid`)`
`ipDict = some_method(*str)`;
Use the StringValueCStr macro to convert a Ruby String into a char* (the rb_str_new functions are for converting in the other direction).
VALUE str = rb_ary_entry(arr, 0); // str is now a Ruby String
char *c_str = StringValueCStr(str);
abc = some_method(c_str);
I was trying to find a substring match in a string, and get the matched position.
I can't figure out what's wrong with the following code:
let str1 = "hello#ﾟДﾟ"
let cmp = "ﾟДﾟ"
let searchRange = Range(start: str1.startIndex, end: str1.endIndex)
let range = str1.rangeOfString(cmp, options: .allZeros, range: searchRange)
println("\(searchRange), \(range!)") // output: 0..<9, 6..<9
let dis = distance(searchRange.startIndex, range!.startIndex) // fatal error: can not increment endIndex! reason: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0).
// let dis = distance(searchRange.startIndex, range!.endIndex) // This will go and output: distance=7
println("distance=\(dis)")
As the comments suggested, although the range had valid values, the distance() method threw a fatal error.
If I'm wrong about the use of distance(), what method should I use to archive the target?
Any advice would be helpful. Thanks.
range!.startIndex points here:
"hello#ﾟДﾟ"
^
But, in this case, #ﾟ is a single character in Swift.
Therefore, This code:
for var idx = searchRange.startIndex; idx != range!.startIndex; idx = idx.successor() {
println("\(idx): \(str1[idx])");
}
prints:
0: h
1: e
2: l
3: l
4: o
5: #ﾟ
7: Дﾟ
fatal error: Can't form a Character from an empty String
// and emits BAD_INSTRUCTION exception
As you can see range!.startIndex never matches to the character boundaries, and the for loop run out the string. That's why you see the exception.
In theory, since String is considered as "Collection of Characters" in Swift, "ﾟДﾟ" should not be a substring of "hello#ﾟДﾟ".
I think .rangeOfString() uses NSString implementation which treats string as a sequence of unichar. I don't know this should be considered as a bug or not.
Try this:
func search<C: CollectionType where C.Generator.Element: Equatable>(col1: C, col2: C) -> C.Index? {
if col2.startIndex == col2.endIndex {
return col1.startIndex
}
var col1Ind = col1.startIndex
while col1Ind != col1.endIndex {
var ind1 = col1Ind
var ind2 = col2.startIndex
while col1[ind1] == col2[ind2] {
++ind1; ++ind2
if ind2 == col2.endIndex { return col1Ind }
if ind1 == col1.endIndex { return nil }
}
++col1Ind
}
return nil
}
Searches for the first instance of the col2 sequence in col1. If found, returns the index of the start of the sub-sequence. If not found, returns nil. If col2 is empty, returns the startIndex of col1.
I am in the process of learning D (I decided it would be a better beginner friendly language than C++) and I decided to give myself the excercise of implementing a general quicksort in D. My program runs fine when sorting integers but it doesn't compile and throws a strange error when sorting strings.
Here is my code:
import std.stdio, std.algorithm;
T[] quickSort(T)(T[] input) {
if (input.length <= 1) {return input;}
ulong i = input.length/2;
auto pivot = input[i];
input = input.remove(i);
T[] lesser = [];
T[] greater = [];
foreach (x; input) {
if (x<=pivot)
{
lesser ~= x;
}
else
{
greater ~=x;
}
}
return (quickSort(lesser) ~ cast(T)pivot ~ quickSort(greater));
}
void main() {
//Sort integers, this works fine
//writeln(quickSort([1,4,3,2,5]));
//Sort string, throws weird error
writeln(quickSort("oidfaosnuidafpsbufiadsb"));
}
When I run it on a string it throws this error:
/usr/share/dmd/src/phobos/std/algorithm.d(7397): Error: template std.algorithm.move does not match any function template declaration. Candidates are:
/usr/share/dmd/src/phobos/std/algorithm.d(1537): std.algorithm.move(T)(ref T source, ref T target)
/usr/share/dmd/src/phobos/std/algorithm.d(1630): std.algorithm.move(T)(ref T source)
/usr/share/dmd/src/phobos/std/algorithm.d(1537): Error: template std.algorithm.move cannot deduce template function from argument types !()(dchar, dchar)
/usr/share/dmd/src/phobos/std/algorithm.d(7405): Error: template std.algorithm.moveAll does not match any function template declaration. Candidates are:
/usr/share/dmd/src/phobos/std/algorithm.d(1786): std.algorithm.moveAll(Range1, Range2)(Range1 src, Range2 tgt) if (isInputRange!(Range1) && isInputRange!(Range2) && is(typeof(move(src.front, tgt.front))))
/usr/share/dmd/src/phobos/std/algorithm.d(7405): Error: template std.algorithm.moveAll(Range1, Range2)(Range1 src, Range2 tgt) if (isInputRange!(Range1) && isInputRange!(Range2) && is(typeof(move(src.front, tgt.front)))) cannot deduce template function from argument types !()(string, string)
helloworld.d(9): Error: template instance std.algorithm.remove!(cast(SwapStrategy)2, string, ulong) error instantiating
helloworld.d(31): instantiated from here: quickSort!(immutable(char))
helloworld.d(31): Error: template instance helloworld.quickSort!(immutable(char)) error instantiating
the problem is that strings are immutable so remove won't work (as it manipulates the string)
you can fix that by not removing and not inserting the pivot in the concat:
auto pivot = input[i];
//input = input.remove(i); //<- remove this line
T[] lesser = [];
//...
return (quickSort(lesser) ~ quickSort(greater)); //<- remove cast(T)pivot ~
or by passing in a dup:
writeln(quickSort("oidfaosnuidafpsbufiadsb".dup));
You have to put a "d" behind the string to make it utf-32, otherwise remove won't accept it.
writeln(quickSort("oidfaosnuidafpsbufiadsb"d.dup));