Structures

Struct Syntax

Slice supports structures containing one or more named fields of arbitrary type, including user-defined complex types. For example:

module M
{
    struct TimeOfDay
    {
        short hour;         // 0 - 23
        short minute;       // 0 - 59
        short second;       // 0 - 59
    }
}

As in C++, this definition introduces a new type called TimeOfDay. Structure definitions form a scope, so the names of the structure fields need to be unique only within their enclosing structure.

Field definitions using a named type are the only construct that can appear inside a structure. It is impossible to, for example, define a structure inside a structure:

struct TwoPoints 
{
    struct Point      // Illegal!
    {            
        short x;
        short y;
    }
    Point coord1;
    Point coord2;
}

This rule applies to Slice in general: type definitions cannot be nested (except for modules, which do support nesting). The reason for this rule is that nested type definitions can be difficult to implement for some target languages and, even if implementable, greatly complicate the scope resolution rules. For a specification language, such as Slice, nested type definitions are unnecessary – you can always write the above definitions as follows (which is stylistically cleaner as well):

Slice

struct Point
{ 
    short x;
    short y;
}

struct TwoPoints      // Legal (and cleaner!)
{   
    Point coord1;
    Point coord2;
}

Language Mapping

A Slice structure maps to a JavaScript type with the same name. For each Slice field, the JavaScript instance contains a corresponding field. As an example, here is our Employee structure once more:

struct Employee
{
    long number;
    string firstName;
    string lastName;
}

The mapping for this structure is equivalent to the following JavaScript code:

// Generated JavaScript code

class Employee {
    function(number = 0n, firstName = "", lastName = "") {
        this.number = number;
        this.firstName = firstName;
        this.lastName = lastName;
    }
}

// Generated TypeScript definition

class Employee {
    constructor(number?: bigint, firstName?: string, lastName?: string);
    clone():Employee;
    equals(other: any): boolean;
    hashCode(): number;
  
    number:bigint;
    firstName:string;
    lastName:string;
}

The generated class defines an equals method for comparison purposes and a clone method to create a shallow copy. For structures that are also legal dictionary key types, the mapped class also defines a hashCode function as required by the Ice.HashMap type.

Generated Constructor

The generated constructor has one parameter for each field. This allows you to construct and initialize an instance in a single statement (instead of first having to construct the instance and then assign to its fields).

All these parameters have also default values (see Fields).

See Also

• Fields

• Classes