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fieldtype

fieldtype(T, name::Symbol | index::Int)

Determine the declared type of a field (specified by name or index) in a composite DataType T.

Examples

In the Julia programming language, the fieldtype function is used to determine the declared type of a field in a composite DataType T. It takes either the field name as a Symbol or the field index as an Int as arguments.

1. Get the type of a named field:

   julia> struct Person
             name::String
             age::Int
             height::Float64
         end
   
   julia> fieldtype(Person, :name)
   String

   This example retrieves the type of the name field in the Person struct, which is String.

2. Get the type of a field using index:

   julia> struct Point
             x::Float64
             y::Float64
             z::Float64
         end
   
   julia> fieldtype(Point, 2)
   Float64

   Here, we obtain the type of the field at index 2 (y) in the Point struct, which is Float64.

3. Handle edge cases when accessing non-existent fields:

   julia> struct Car
             brand::String
             model::String
         end
   
   julia> fieldtype(Car, :color)
   ERROR: type Car has no field color

   In this example, attempting to access a non-existent field (color) in the Car struct results in an error. Make sure to provide a valid field name or index to avoid such errors.

Common mistake example:

julia> struct Book
           title::String
           author::String
       end

julia> fieldtype(Book, "author")
ERROR: MethodError: no method matching fieldtype(::Type{Book}, ::String)

In this example, the field name is provided as a string ("author") instead of a symbol (:author). It's important to use the correct format for the field name to retrieve the type successfully.

See Also

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