Reference: PLT Scheme

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`` | Running PLT Scheme
| Bibliography
| Index

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make-weak-box
weak-box-value
weak-box?

Version: 4.0.2
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#### 15.1`` Weak Boxes

A weak box is similar to a normal box (see Boxes), but when the garbage collector (see Garbage Collection) can prove that the content value of a weak box is only reachable via weak references, the content of the weak box is replaced with #f. A weak reference is a reference through a weak box, through a key reference in a weak hash table (see Hash Tables), through a value in an ephemeron where the value can be replaced by #f (see Ephemerons), or through a custodian (see Custodians).

(make-weak-box v) → weak-box?
v : any/c

Returns a new weak box that initially contains v.

(weak-box-value weak-box) → any
weak-box : weak-box?

Returns the value contained in weak-box. If the garbage collector has proven that the previous content value of weak-box was reachable only through a weak reference, then #f is returned.

(weak-box? v) → boolean?
v : any/c

Returns #t if v is a weak box, #f otherwise.

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