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Nullable

Nullable(x)

Wrap value x in an object of type Nullable, which indicates whether a value is present. Nullable(x) yields a non-empty wrapper, and Nullable{T}() yields an empty instance of a wrapper that might contain a value of type T.

Examples

1. Wrap a value in a Nullable object:

   julia> nullable_value = Nullable(42)
   Nullable{Int64}(42)

   This example wraps the value 42 in a Nullable object of type Int64.

2. Create an empty Nullable object:

   julia> nullable_empty = Nullable{Float64}()
   Nullable{Float64}()

   This example creates an empty Nullable object of type Float64 that does not contain any value.

3. Check if a Nullable object is empty:

   julia> nullable_value = Nullable("Julia")
   Nullable{String}("Julia")
   julia> isnull(nullable_value)
   false
   julia> nullable_empty = Nullable{Bool}()
   Nullable{Bool}()
   julia> isnull(nullable_empty)
   true

   isnull can be used to check if a Nullable object is empty or contains a value.

Common mistake example:

julia> nullable_value = Nullable()
ERROR: MethodError: no method matching Nullable()

In this example, the Nullable function is called without providing a value or specifying a type. The correct usage is either Nullable(x) to wrap a value or Nullable{T}() to create an empty Nullable object with a specified type.

See Also

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