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Interface: StructFieldOptions

Per-field options, the third element of a StructField entry.

Properties​

asPointer?​

optional asPointer?: boolean

For a nested StructDef field: store the address of a buffer of its own instead of laying the struct out inline, i.e. C's struct limits *. A null pointer unpacks as null.

condition?​

optional condition?: () => boolean

Answered once, when the struct is defined: a field whose condition returns false is not part of the struct at all, so it neither shows up in the layout nor shifts the fields after it. This is how a member only some platforms have is expressed.

Returns​

boolean

default?​

optional default?: any

Value to pack when the field is absent from the object. Absent means undefined: null is a value a 'pointer' or 'cstring' field takes, and is packed as a null address. Wins over optional.

lengthOf?​

optional lengthOf?: string

Names the field this one holds the element count of — a [ elementType ] field, or a 'cstring' field, which pairs into C's counted string. The count is written by the field it counts, so this field's own value is never read from the object being packed, and default, optional, validate and packTransform are rejected on it.

optional?​

optional optional?: boolean

When true, an absent field is zeroed instead of throwing — which unpacks back as 0, false, or null for a pointer or a string.

packTransform?​

optional packTransform?: (value) => any

Maps the value the caller gave to the one the field stores.

Parameters​

value​

any

Returns​

any

unpackTransform?​

optional unpackTransform?: (value) => any

Maps the stored value back on the way out of unpack.

Parameters​

value​

any

Returns​

any

validate?​

optional validate?: StructValidator | StructValidator[]

One validator, or a list of them; every one runs.