Record types

Record types { ... } are simple property records. Record types are memory-efficient in cost of a hash-map-like field access.

Note: The decision for having record types compiling into hash-map structures is because these types use to contain many fields, for instance, in Whack DS components and in operations requiring a large number of options.

type N1 = { x : decimal, y : decimal };

type N2 = {
    /** x */
    x:double,

    /** y */
    y?:boolean,
};

Note: Record types do not match with types structurally unlike in structural-type-first languages. They are simply structures the user may express inline.

Version control

Fields of a record type may be tied to a namespace, which is useful for version control.

// ===== Flexible.es =====

package = com.example.product;

/**
 * Flexible version control namespace.
 */
public namespace Flexible = "http://business.com/product/flexible";

// ===== Judgement.es =====

package = com.example.product;

/**
 * Judgement version control namespace.
 */
public namespace Judgement = "http://business.com/product/judgement";

// ===== Pair.es =====

package = com.example.product;

/**
 * Pair.
 */
public type Pair = {
    Flexible::strength : [decimal],
    Judgement::strength : [decimal],
};

Field omission

All fields are required unless they contain undefined or null. A field such as x?:T is equivalent to x:(void, T).

Field order

Due to sensitive field order, record types with equivalent fields but in different orders will be incompatible.

Writing ESDoc comments

Fields may have a preceding ESDoc comment, as in:

type R = {
    /**
     * Comment.
     */
    x : double,
};

Compatibility

Two record types are compatible only if either a) one is used as a subset of another or b) fields are equivalent and appear in the same order.

Rest

One trailing ...rest component may appear in a record, where rest must be another record type. The resulting type is a subtype of rest and properties must not collide.

// A
type A = { x:double };
// B < A
type B = { y:double, ...A };