5.6 Structure Utilities (original) (raw)

5.6 Structure Utilities🔗ℹ

Creates a vector representing v. The first slot of the result vector contains a symbol whose printed name has the formstruct:id. Each remaining slot contains either the value of a field in v, if it is accessible via the current inspector, or opaque-v for a field that is not accessible. A single opaque-v value is used in the vector for contiguous inaccessible fields. (Consequently, the size of the vector does not match the size of the struct if more than one field is inaccessible.)

Returns #t ifstruct-info exposes any structure types of v with the current inspector, #f otherwise.

Typically, when (struct? v) is true, then(struct->vector v) exposes at least one field value. It is possible, however, for the only visible types of v to contribute zero fields.

Returns #t ifv is a structure type descriptor value, #fotherwise.

Returns#t if v is a constructor procedure generated bystruct or make-struct-type, #fotherwise.

Returns#t if v is a predicate procedure generated bystruct or make-struct-type, #fotherwise.

Returns #f if v is not an instance of aprefab structure type. Otherwise, the result is the shorted key that could be used with make-prefab-struct to create an instance of the structure type.

Examples:

> (prefab-struct-key #s(cat "Garfield"))

'cat

> (struct cat (name) #:prefab)

> (struct cute-cat cat (shipping-dest) #:prefab)

> (cute-cat "Nermel" "Abu Dhabi")

'#s((cute-cat cat 1) "Nermel" "Abu Dhabi")

> (prefab-struct-key (cute-cat "Nermel" "Abu Dhabi"))

'(cute-cat cat 1)

> (prefab-struct-key #s(cat "Garfield"))
'cat
> (struct cat (name) #:prefab)
> (struct cute-cat cat (shipping-dest) #:prefab)
> (cute-cat "Nermel" "Abu Dhabi")
'#s((cute-cat cat 1) "Nermel" "Abu Dhabi")
> (prefab-struct-key (cute-cat "Nermel" "Abu Dhabi"))
'(cute-cat cat 1)

Creates an instance of a prefab structure type, using thevs as field values. The key and the number ofvs determine the prefab structure type.

A key identifies a structure type based on a list with the following items:

A symbol for the structure type’s name.
An exact, nonnegative integer representing the number of non-automatic fields in the structure type, not counting fields from the supertype (if any).
A list of two items, where the first is an exact, nonnegative integer for the number of automatic fields in the structure type that are not from the supertype (if any), and the second element is an arbitrary value that is the value for the automatic fields.
A vector of exact, nonnegative integers that indicate mutable non-automatic fields in the structure type, counting from0 and not including fields from the supertype (if any).
Nothing else, if the structure type has no supertype. Otherwise, the rest of the list is the key for the supertype.

An empty vector and an auto-field list that starts with 0 can be omitted. Furthermore, the first integer (which indicates the number of non-automatic fields) can be omitted, since it can be inferred from the number of supplied vs. Finally, a single symbol can be used instead of a list that contains only a symbol (in the case that the structure type has no supertype, no automatic fields, and no mutable fields).

The total field count must be no more than 32768. If the number of fields indicated by key is inconsistent with the number of supplied vs, the exn:fail:contract exception is raised.

Examples:

> (make-prefab-struct 'clown "Binky" "pie")

'#s(clown "Binky" "pie")

> (make-prefab-struct '(clown 2) "Binky" "pie")

'#s(clown "Binky" "pie")

> (make-prefab-struct '(clown 2 (0 #f) #()) "Binky" "pie")

'#s(clown "Binky" "pie")

> (make-prefab-struct '(clown 1 (1 #f) #()) "Binky" "pie")

'#s((clown (1 #f)) "Binky" "pie")

> (make-prefab-struct '(clown 1 (1 #f) #(0)) "Binky" "pie")

'#s((clown (1 #f) #(0)) "Binky" "pie")

> (make-prefab-struct 'clown "Binky" "pie")
'#s(clown "Binky" "pie")
> (make-prefab-struct '(clown 2) "Binky" "pie")
'#s(clown "Binky" "pie")
> (make-prefab-struct '(clown 2 (0 #f) #()) "Binky" "pie")
'#s(clown "Binky" "pie")
> (make-prefab-struct '(clown 1 (1 #f) #()) "Binky" "pie")
'#s((clown (1 #f)) "Binky" "pie")
> (make-prefab-struct '(clown 1 (1 #f) #(0)) "Binky" "pie")
'#s((clown (1 #f) #(0)) "Binky" "pie")

Returns a pair containing the prefab key and field count for the structure type descriptor type if it represents a prefab structure type, #f otherwise.

Added in version 8.5.0.8 of package base.

If the number of fields indicated by key is inconsistent withfield-count, the exn:fail:contract exception is raised.

Return #t if v can be a prefab structure type key, #f otherwise.

See make-prefab-struct for a description of valid key shapes.

5.6.1 Additional Structure Utilities🔗ℹ

The bindings documented in this section are provided by the racket/struct library, not racket/base or racket.

Produces a function suitable as a value forgen:custom-write or prop:custom-write. The function prints values in “constructor style.” When the value is printed as an expression, it is shown as an application of the constructor (as returned byget-constructor) to the contents (as returned byget-contents). When given to write, it is shown as an unreadable value with the constructor separated from the contents by a colon.

Examples:

> (print (point 1 2))

(point 1 2)

> (write (point 1 2))

#<point: 1 2>

> (print (point 1 2))
(point 1 2)
> (write (point 1 2))
#<point: 1 2>

The function also cooperates with pretty-print:

#<point: 3000000 4000000>

Note that the printer uses a separate property,prop:custom-print-quotable, to determine whether a struct instance is quotable. If so, the printer may print it inwrite mode it in certain contexts, such as within a list. For example:

> (print (list (point 1 2) (point 3 4)))

'(#<point: 1 2> #<point: 3 4>)

> (print (list (point 1 2) (point 3 4)))
'(#<point: 1 2> #<point: 3 4>)

Use #:property prop:custom-print-quotable 'never to prevent a struct instance from being considered quotable. For example:

> (print (list (point2 1 2) (point2 3 4)))

(list (point 1 2) (point 3 4))

> (print (list (point2 1 2) (point2 3 4)))
(list (point 1 2) (point 3 4))

Keyword arguments can be simulated with unquoted-printing-string:

Added in version 6.3 of package base.

(struct->list v [#:on-opaque on-opaque]) → (or/c list? #f)

v : any/c

on-opaque : (or/c 'error 'return-false 'skip) = 'error

(struct->list v [#:on-opaque on-opaque]) → (or/c list? #f)
v : any/c
on-opaque : (or/c 'error 'return-false 'skip) = 'error

Returns a list containing the struct instance v’s fields. Unlike struct->vector, the struct name itself is not included.

If any fields of v are inaccessible via the current inspector the behavior of struct->list is determined byon-opaque. If on-opaque is 'error (the default), an error is raised. If it is 'return-false,struct->list returns #f. If it is 'skip, the inaccessible fields are omitted from the list.

Examples:

> (struct open (u v) #:transparent)

> (struct->list (open 'a 'b))

'(a b)

> (struct->list #s(pre 1 2 3))

'(1 2 3)

> (struct secret open (x y))

> (struct->list (secret 0 1 17 22))

struct->list: expected argument of type ;

given: (secret 0 1 ...)

> (struct->list (secret 0 1 17 22) #:on-opaque 'return-false)

#f

> (struct->list (secret 0 1 17 22) #:on-opaque 'skip)

'(0 1)

> (struct->list 'not-a-struct #:on-opaque 'return-false)

#f

> (struct->list 'not-a-struct #:on-opaque 'skip)

'()

> (struct open (u v) #:transparent)
> (struct->list (open 'a 'b))
'(a b)
> (struct->list #s(pre 1 2 3))
'(1 2 3)
> (struct secret open (x y))
> (struct->list (secret 0 1 17 22))
struct->list: expected argument of type ;
given: (secret 0 1 ...)
> (struct->list (secret 0 1 17 22) #:on-opaque 'return-false)
#f
> (struct->list (secret 0 1 17 22) #:on-opaque 'skip)
'(0 1)
> (struct->list 'not-a-struct #:on-opaque 'return-false)
#f
> (struct->list 'not-a-struct #:on-opaque 'skip)
'()

Added in version 6.3 of package base.