13.9 Structure Inspectors

► |  | Reference: Racket

1 | Language Model
2 | Syntactic Forms
3 | Datatypes
4 | Structures
5 | Classes and Objects
6 | Units
7 | Contracts
8 | Pattern Matching
9 | Control Flow
10 | Concurrency
11 | Macros
12 | Input and Output
13 | Reflection and Security
14 | Operating System
15 | Memory Management
16 | Unsafe Operations
17 | Running Racket
| Bibliography
| Index

▼ | 13 | Reflection and Security

13.1 | Namespaces
13.2 | Evaluation and Compilation
13.3 | The racket/ load Language
13.4 | Module Names and Loading
13.5 | Proxies and Chaperones
13.6 | Security Guards
13.7 | Custodians
13.8 | Thread Groups
13.9 | Structure Inspectors
13.10 | Code Inspectors
13.11 | Sandboxed Evaluation

On this page:

inspector?
make-inspector
make-sibling-inspector
current-inspector
struct-info
struct-type-info
struct-type-make-constructor
struct-type-make-predicate
object-name

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#### 13.9`` Structure Inspectors

An inspector provides access to structure fields and structure type information without the normal field accessors and mutators. (Inspectors are also used to control access to module bindings; see Code Inspectors.) Inspectors are primarily intended for use by debuggers.

When a structure type is created, an inspector can be supplied. The given inspector is not the one that will control the new structure type; instead, the given inspector’s parent will control the type. By using the parent of the given inspector, the structure type remains opaque to “peer” code that cannot access the parent inspector.

The current-inspector parameter determines a default inspector argument for new structure types. An alternate inspector can be provided though the #:inspector option of the define-struct form (see Defining Structure Types: struct), or through an optional inspector argument to make-struct-type.

( inspector? v) → boolean?
v : any/c

Returns #t if v is an inspector, #f otherwise.

( make-inspector [inspector]) → inspector?
inspector : inspector? = ( current-inspector)

Returns a new inspector that is a subinspector of inspector. Any structure type controlled by the new inspector is also controlled by its ancestor inspectors, but no other inspectors.

( make-sibling-inspector [inspector]) → inspector?
inspector : inspector? = ( current-inspector)

Returns a new inspector that is a subinspector of the same inspector as inspector. That is, inspector and the result inspector control mutually disjoint sets of structure types.

( current-inspector) → inspector?
( current-inspector insp) → void?
insp : inspector?

A parameter that determines the default inspector for newly created structure types.

( struct-info v)

→

( or/c struct-type? #f) |  | boolean?

v : any/c

Returns two values:

- struct-type: a structure type descriptor or #f; the result is a structure type descriptor of the most specific type for which v is an instance, and for which the current inspector has control, or the result is #f if the current inspector does not control any structure type for which the struct is an instance.

- skipped?: #f if the first result corresponds to the most specific structure type of v, #t otherwise.

( struct-type-info struct-type)

→

symbol?
exact-nonnegative-integer?
exact-nonnegative-integer?
struct-accessor-procedure?
struct-mutator-procedure?
( listof exact-nonnegative-integer?)
( or/c struct-type? #f)
boolean?

struct-type : struct-type?

Returns eight values that provide information about the structure type descriptor struct-type, assuming that the type is controlled by the current inspector:

- name: the structure type’s name as a symbol;

- init-field-cnt: the number of fields defined by the structure type provided to the constructor procedure (not counting fields created by its ancestor types);

- auto-field-cnt: the number of fields defined by the structure type without a counterpart in the constructor procedure (not counting fields created by its ancestor types);

- accessor-proc: an accessor procedure for the structure type, like the one returned by make-struct-type;

- mutator-proc: a mutator procedure for the structure type, like the one returned by make-struct-type;

- immutable-k-list: an immutable list of exact non-negative integers that correspond to immutable fields for the structure type;

- super-type: a structure type descriptor for the most specific ancestor of the type that is controlled by the current inspector, or #f if no ancestor is controlled by the current inspector;

- skipped?: #f if the seventh result is the most specific ancestor type or if the type has no supertype, #t otherwise.

If the type for struct-type is not controlled by the current inspector, the exn:fail:contract exception is raised.

( struct-type-make-constructor struct-type)
→ struct-constructor-procedure?
struct-type : struct-type?

Returns a constructor procedure to create instances of the type for struct-type. If the type for struct-type is not controlled by the current inspector, the exn:fail:contract exception is raised.

( struct-type-make-predicate struct-type) → any
struct-type : any/c

Returns a predicate procedure to recognize instances of the type for struct-type. If the type for struct-type is not controlled by the current inspector, the exn:fail:contract exception is raised.

( object-name v) → any
v : any/c

Returns a value for the name of v if v has a name, #f otherwise. The argument v can be any value, but only (some) procedures, structures, structure types, structure type properties, regexp values, and ports have names. See also Inferred Value Names.

The name (if any) of a procedure is always a symbol. The procedure-rename function creates a procedure with a specific name.

The name of a structure, structure type, structure type property is always a symbol. If a structure is a procedure as implemented by one of its fields (i.e., the prop:procedure property value for the structure’s type is an integer), then its name is the implementing procedure’s name; otherwise, its name matches the name of the structure type that it instantiates.

The name of a regexp value is a string or byte string. Passing the string or byte string to regexp, byte-regexp, pregexp, or byte-pregexp (depending on the kind of regexp whose name was extracted) produces a value that matches the same inputs.

The name of a port can be any value, but many tools use a path or string name as the port’s for (to report source locations, for example).

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