Difference between revisions of "W1035 Not a Value"
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* [[W1033 Character Encoding]] | * [[W1033 Character Encoding]] | ||
== Introduction == | == Introduction == | ||
There's often a need to represent the ''absence'' of a value. For example, consider a database tracking students' first name, middle | There's often a need to represent the ''absence'' of a value. For example, consider a database tracking students' first name, middle name, and last name. Not all students have a middle name. So what value should we store in a variable representing a student's middle name if this particular student doesn't have one? | ||
The name of this special value, representing ''non-existence'', varies from language to language. In Swift, it's called '''nil'''. | The name of this special value, representing ''non-existence'', varies from language to language. In Swift, it's called '''nil'''. |
Revision as of 23:10, 7 November 2019
Prerequisites[edit]
Introduction[edit]
There's often a need to represent the absence of a value. For example, consider a database tracking students' first name, middle name, and last name. Not all students have a middle name. So what value should we store in a variable representing a student's middle name if this particular student doesn't have one?
The name of this special value, representing non-existence, varies from language to language. In Swift, it's called nil.
Nil[edit]
Nil represents the absence of value of the specified type. We indicate that we intend to accept such nil values by specifying the type explicitly and suffixing the type name with a question mark. For example, in the aforementioned case, rather than specify the type as:
let middleName : Character
we use:
let middleName : Character?
This enables us to specify either a character or the special place-holder for no value, nil:
let middleName : Character? = "A"
-or-
let middleName : Character? = nil