【Swift 60秒】88 - Unwrapping optionals
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0x00 Lesson
Optional strings might contain
a string like “Hello” or they might be nil
- nothing at all.
Consider this optional string:
vaf name: String? = nil
What happens if we use name.count
? A real string has a count
property that stores how many letters it has, but this is nil
- it’s empty memory, not a string, so it doesn’t have a count
.
Because of this, trying to read name.count
is unsafe and Swift won’t allow it. Instead, we must look inside the optional and see what’s there - a process known as unwrapping
.
A common way of unwrapping optionals is with if let
syntax, which unwraps with a condition. If there was a value inside the optional then you can use it, but if there wasn’t the condition fails.
For example:
if let unwrapped = name {
print("\(unwrapped.count) letters")
} else {
print("Missing name.")
}
if name
holds a string, it will be put inside unwrapped
as a regular String
and we can read its count
property inside the condition. Alternatively, if name
is empty, the else
code will be run.
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