Struct

new to Analytica 7.0

Struct class

A Struct object defines a new atomic data type. A struct appears on a diagram with a shape that resembles a function shape, but with flat midsections on both the left and right.

After you have introduced a Struct, you can create instances of the struct. Each of those instances is atomic and immutable. The instance is atomic in the sense that Array Abstraction treats it as a single cell. It is immutable in the sense that once an instance is instantiated, it cannot be destructively altered.

A struct instance can have multiple member fields, each of which can have a different data type and dimensionality. For example, a single struct could have a scalar member, a 1-D member and a 2-D member, where the dimensions of the members are unrelated. The indexes of each member do not combine.

Note that a Struct is an Object, an instance of a struct is a Value.

Defining a Struct

To define a new data type, you create an object whose class is Struct. You can do this by first creating a user function object, and then in its Object window, changing its class to Struct.

Like a User-Defined Function (UDF), a Struct uses the Parameters attribute with precisely the same Function Parameter Qualifiers as a UDF. One example would be:

Struct MyDtype( a : atom ; b : Text [I] ; c: Number[J] )

This data type has three members -- a, b, and c. The a field can have any atomic data type, the b member must be text and is allowed to have the index I, and the c member must be a numeric and is allowed to have index J.

The default Definition of a Struct is Self. Sometimes it makes sense to include a more specialized definition -- see #Constructor customization below.

Instantiating a value

To create an instance of a Struct (an atomic value), you simply call the name of your struct as if it were a function from within an expression. In the previous example, that might be:

MyDtype( Category, Category_aliases, Category_IDs )

If there are extra dimensions in any of the values passed to the constructor parameters, Array Abstraction will kick in and you'll end up with multiple struct instances, each instance being one cell in the array-values result.