IntValue ?? 0 == -1? “-”: “+” What does this mean?
I am importing price information and adding + or -.
I put the title code in print () and it works but I do not know what it means.
print("(IntValue ?? 0 == -1 ? "-" : "+")")
Please explain it briefly to me.
swift ternary-operator
asked Nov 23 '18 at 2:36
EnkhaEnkha
17411
add a comment |
I am importing price information and adding + or -.
I put the title code in print () and it works but I do not know what it means.
print("(IntValue ?? 0 == -1 ? "-" : "+")")
Please explain it briefly to me.
swift ternary-operator
asked Nov 23 '18 at 2:36
EnkhaEnkha
17411
add a comment |
I am importing price information and adding + or -.
I put the title code in print () and it works but I do not know what it means.
print("(IntValue ?? 0 == -1 ? "-" : "+")")
Please explain it briefly to me.
swift ternary-operator
asked Nov 23 '18 at 2:36
EnkhaEnkha
17411
I am importing price information and adding + or -.
I put the title code in print () and it works but I do not know what it means.
print("(IntValue ?? 0 == -1 ? "-" : "+")")
Please explain it briefly to me.
swift ternary-operator
swift ternary-operator
asked Nov 23 '18 at 2:36
EnkhaEnkha
17411
asked Nov 23 '18 at 2:36
EnkhaEnkha
17411
edited Nov 23 '18 at 4:40
Enkha
asked Nov 23 '18 at 2:36
EnkhaEnkha
17411
asked Nov 23 '18 at 2:36
EnkhaEnkha
17411
asked Nov 23 '18 at 2:36
EnkhaEnkha
17411
17411
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
The variable IntValue is an optional, which means its either an Integer or nil. IntValue ?? 0 means that if IntValue exists, then use the value of IntValue. If IntValue is nil, then use the value 0. Next, compare that value with -1. If that value is equal to -1, then print -. If that value does not equal -1, then print +.
Here's equivalent code with only if statements:
var defaultInt = 0
if IntValue != nil {
defaultInt = IntValue! // force unwrap the optional value
}
if defaultInt == -1 {
print("-")
}
else {
print("+")
}
answered Nov 23 '18 at 2:51
Kevin BaiKevin Bai
18817
I think it should beif IntValue != nilas you only want to use the value ofIntValueif it’s notnil; otherwise use0
– War10ck
Nov 23 '18 at 3:55
War10ck is right. That line should beif IntValue != nil
– Duncan C
Nov 23 '18 at 11:07
Oops, you guys are right. Fixed it in the edit.
– Kevin Bai
Nov 23 '18 at 11:14
add a comment |
Kevin's answer is very good.
Some background that helps explain further:
The code you posted uses two rather cryptic operators together.
?? is the nil-coalescing operator.
It takes an optional value, which can contain nil, and provides a new value to use when it does contain nil.
Edit:
(Note that you can skip the nil-coalescing operator and use IntValue == -1 instead. That works because only a non-nil value of -1 is equal to -1. An optional that contains nil is not equal to -1.
You could rewrite the line as
print("(IntValue == -1 ? "-" : "+")")
And get the same result.)
The next tricky bit is the "ternary operator". This comes from C. It's quite cryptic, but also quite useful.
It takes the form boolean ? value_for_true : value_for_false
Where boolean is a boolean expression that evaluates to true or false.
If boolean is true, then the result of the whole ternary expression is the value_for_true sub-expression.
If boolean is false the result of the whole ternary expression is the value_for_false sub-expression.
IntValue ?? 0 == -1 is the boolean part of your ternary expression. It evaluates as true if IntValue is -1. It evaluates as false if IntValue contains any other value, or if it contains nil.
(Note that variables and let constants should start with lower-case letters, so IntValue should be intValue.)
answered Nov 23 '18 at 3:07
Duncan CDuncan C
93.7k13114200
I voted for you. Additional explanation Thank you.
– Enkha
Nov 23 '18 at 4:41
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
The variable IntValue is an optional, which means its either an Integer or nil. IntValue ?? 0 means that if IntValue exists, then use the value of IntValue. If IntValue is nil, then use the value 0. Next, compare that value with -1. If that value is equal to -1, then print -. If that value does not equal -1, then print +.
Here's equivalent code with only if statements:
var defaultInt = 0
if IntValue != nil {
defaultInt = IntValue! // force unwrap the optional value
}
if defaultInt == -1 {
print("-")
}
else {
print("+")
}
answered Nov 23 '18 at 2:51
Kevin BaiKevin Bai
18817
I think it should beif IntValue != nilas you only want to use the value ofIntValueif it’s notnil; otherwise use0
– War10ck
Nov 23 '18 at 3:55
War10ck is right. That line should beif IntValue != nil
– Duncan C
Nov 23 '18 at 11:07
Oops, you guys are right. Fixed it in the edit.
– Kevin Bai
Nov 23 '18 at 11:14
add a comment |
The variable IntValue is an optional, which means its either an Integer or nil. IntValue ?? 0 means that if IntValue exists, then use the value of IntValue. If IntValue is nil, then use the value 0. Next, compare that value with -1. If that value is equal to -1, then print -. If that value does not equal -1, then print +.
Here's equivalent code with only if statements:
var defaultInt = 0
if IntValue != nil {
defaultInt = IntValue! // force unwrap the optional value
}
if defaultInt == -1 {
print("-")
}
else {
print("+")
}
answered Nov 23 '18 at 2:51
Kevin BaiKevin Bai
18817
I think it should beif IntValue != nilas you only want to use the value ofIntValueif it’s notnil; otherwise use0
– War10ck
Nov 23 '18 at 3:55
War10ck is right. That line should beif IntValue != nil
– Duncan C
Nov 23 '18 at 11:07
Oops, you guys are right. Fixed it in the edit.
– Kevin Bai
Nov 23 '18 at 11:14
add a comment |
The variable IntValue is an optional, which means its either an Integer or nil. IntValue ?? 0 means that if IntValue exists, then use the value of IntValue. If IntValue is nil, then use the value 0. Next, compare that value with -1. If that value is equal to -1, then print -. If that value does not equal -1, then print +.
Here's equivalent code with only if statements:
var defaultInt = 0
if IntValue != nil {
defaultInt = IntValue! // force unwrap the optional value
}
if defaultInt == -1 {
print("-")
}
else {
print("+")
}
answered Nov 23 '18 at 2:51
Kevin BaiKevin Bai
18817
The variable IntValue is an optional, which means its either an Integer or nil. IntValue ?? 0 means that if IntValue exists, then use the value of IntValue. If IntValue is nil, then use the value 0. Next, compare that value with -1. If that value is equal to -1, then print -. If that value does not equal -1, then print +.
Here's equivalent code with only if statements:
var defaultInt = 0
if IntValue != nil {
defaultInt = IntValue! // force unwrap the optional value
}
if defaultInt == -1 {
print("-")
}
else {
print("+")
}
answered Nov 23 '18 at 2:51
Kevin BaiKevin Bai
18817
edited Nov 23 '18 at 11:19
answered Nov 23 '18 at 2:51
Kevin BaiKevin Bai
18817
answered Nov 23 '18 at 2:51
Kevin BaiKevin Bai
18817
answered Nov 23 '18 at 2:51
Kevin BaiKevin Bai
18817
18817
I think it should beif IntValue != nilas you only want to use the value ofIntValueif it’s notnil; otherwise use0
– War10ck
Nov 23 '18 at 3:55
War10ck is right. That line should beif IntValue != nil
– Duncan C
Nov 23 '18 at 11:07
Oops, you guys are right. Fixed it in the edit.
– Kevin Bai
Nov 23 '18 at 11:14
add a comment |
I think it should beif IntValue != nilas you only want to use the value ofIntValueif it’s notnil; otherwise use0
– War10ck
Nov 23 '18 at 3:55
War10ck is right. That line should beif IntValue != nil
– Duncan C
Nov 23 '18 at 11:07
Oops, you guys are right. Fixed it in the edit.
– Kevin Bai
Nov 23 '18 at 11:14
I think it should be
if IntValue != nil as you only want to use the value of IntValue if it’s not nil; otherwise use 0– War10ck
Nov 23 '18 at 3:55
I think it should be
if IntValue != nil as you only want to use the value of IntValue if it’s not nil; otherwise use 0– War10ck
Nov 23 '18 at 3:55
War10ck is right. That line should be
if IntValue != nil– Duncan C
Nov 23 '18 at 11:07
War10ck is right. That line should be
if IntValue != nil– Duncan C
Nov 23 '18 at 11:07
Oops, you guys are right. Fixed it in the edit.
– Kevin Bai
Nov 23 '18 at 11:14
Oops, you guys are right. Fixed it in the edit.
– Kevin Bai
Nov 23 '18 at 11:14
add a comment |
Kevin's answer is very good.
Some background that helps explain further:
The code you posted uses two rather cryptic operators together.
?? is the nil-coalescing operator.
It takes an optional value, which can contain nil, and provides a new value to use when it does contain nil.
Edit:
(Note that you can skip the nil-coalescing operator and use IntValue == -1 instead. That works because only a non-nil value of -1 is equal to -1. An optional that contains nil is not equal to -1.
You could rewrite the line as
print("(IntValue == -1 ? "-" : "+")")
And get the same result.)
The next tricky bit is the "ternary operator". This comes from C. It's quite cryptic, but also quite useful.
It takes the form boolean ? value_for_true : value_for_false
Where boolean is a boolean expression that evaluates to true or false.
If boolean is true, then the result of the whole ternary expression is the value_for_true sub-expression.
If boolean is false the result of the whole ternary expression is the value_for_false sub-expression.
IntValue ?? 0 == -1 is the boolean part of your ternary expression. It evaluates as true if IntValue is -1. It evaluates as false if IntValue contains any other value, or if it contains nil.
(Note that variables and let constants should start with lower-case letters, so IntValue should be intValue.)
answered Nov 23 '18 at 3:07
Duncan CDuncan C
93.7k13114200
I voted for you. Additional explanation Thank you.
– Enkha
Nov 23 '18 at 4:41
add a comment |
Kevin's answer is very good.
Some background that helps explain further:
The code you posted uses two rather cryptic operators together.
?? is the nil-coalescing operator.
It takes an optional value, which can contain nil, and provides a new value to use when it does contain nil.
Edit:
(Note that you can skip the nil-coalescing operator and use IntValue == -1 instead. That works because only a non-nil value of -1 is equal to -1. An optional that contains nil is not equal to -1.
You could rewrite the line as
print("(IntValue == -1 ? "-" : "+")")
And get the same result.)
The next tricky bit is the "ternary operator". This comes from C. It's quite cryptic, but also quite useful.
It takes the form boolean ? value_for_true : value_for_false
Where boolean is a boolean expression that evaluates to true or false.
If boolean is true, then the result of the whole ternary expression is the value_for_true sub-expression.
If boolean is false the result of the whole ternary expression is the value_for_false sub-expression.
IntValue ?? 0 == -1 is the boolean part of your ternary expression. It evaluates as true if IntValue is -1. It evaluates as false if IntValue contains any other value, or if it contains nil.
(Note that variables and let constants should start with lower-case letters, so IntValue should be intValue.)
answered Nov 23 '18 at 3:07
Duncan CDuncan C
93.7k13114200
I voted for you. Additional explanation Thank you.
– Enkha
Nov 23 '18 at 4:41
add a comment |
Kevin's answer is very good.
Some background that helps explain further:
The code you posted uses two rather cryptic operators together.
?? is the nil-coalescing operator.
It takes an optional value, which can contain nil, and provides a new value to use when it does contain nil.
Edit:
(Note that you can skip the nil-coalescing operator and use IntValue == -1 instead. That works because only a non-nil value of -1 is equal to -1. An optional that contains nil is not equal to -1.
You could rewrite the line as
print("(IntValue == -1 ? "-" : "+")")
And get the same result.)
The next tricky bit is the "ternary operator". This comes from C. It's quite cryptic, but also quite useful.
It takes the form boolean ? value_for_true : value_for_false
Where boolean is a boolean expression that evaluates to true or false.
If boolean is true, then the result of the whole ternary expression is the value_for_true sub-expression.
If boolean is false the result of the whole ternary expression is the value_for_false sub-expression.
IntValue ?? 0 == -1 is the boolean part of your ternary expression. It evaluates as true if IntValue is -1. It evaluates as false if IntValue contains any other value, or if it contains nil.
(Note that variables and let constants should start with lower-case letters, so IntValue should be intValue.)
answered Nov 23 '18 at 3:07
Duncan CDuncan C
93.7k13114200
Kevin's answer is very good.
Some background that helps explain further:
The code you posted uses two rather cryptic operators together.
?? is the nil-coalescing operator.
It takes an optional value, which can contain nil, and provides a new value to use when it does contain nil.
Edit:
(Note that you can skip the nil-coalescing operator and use IntValue == -1 instead. That works because only a non-nil value of -1 is equal to -1. An optional that contains nil is not equal to -1.
You could rewrite the line as
print("(IntValue == -1 ? "-" : "+")")
And get the same result.)
The next tricky bit is the "ternary operator". This comes from C. It's quite cryptic, but also quite useful.
It takes the form boolean ? value_for_true : value_for_false
Where boolean is a boolean expression that evaluates to true or false.
If boolean is true, then the result of the whole ternary expression is the value_for_true sub-expression.
If boolean is false the result of the whole ternary expression is the value_for_false sub-expression.
IntValue ?? 0 == -1 is the boolean part of your ternary expression. It evaluates as true if IntValue is -1. It evaluates as false if IntValue contains any other value, or if it contains nil.
(Note that variables and let constants should start with lower-case letters, so IntValue should be intValue.)
answered Nov 23 '18 at 3:07
Duncan CDuncan C
93.7k13114200
edited Nov 23 '18 at 3:13
answered Nov 23 '18 at 3:07
Duncan CDuncan C
93.7k13114200
answered Nov 23 '18 at 3:07
Duncan CDuncan C
93.7k13114200
answered Nov 23 '18 at 3:07
Duncan CDuncan C
93.7k13114200
93.7k13114200
I voted for you. Additional explanation Thank you.
– Enkha
Nov 23 '18 at 4:41
add a comment |
I voted for you. Additional explanation Thank you.
– Enkha
Nov 23 '18 at 4:41
I voted for you. Additional explanation Thank you.
– Enkha
Nov 23 '18 at 4:41
I voted for you. Additional explanation Thank you.
– Enkha
Nov 23 '18 at 4:41
add a comment |
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