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LRU_Cache

container.LRU_Cache

(LM 
type
:
mutate, K 
type
:
property.hashable, V 
type
)
 ref
:
Any
 is
[Private constructor]
LRU_Cache - a mutable cache applying least recently used eviction strategy

It is implemented using a hash map for index lookup and an implicit linked
list that stores elements in order from most to least recently used.

The linked list structure is implemented using arrays for keys, values and
previous/next pointers. This avoids creation and deletion of list node
objects, instead only the values in the pointer array need to be updated when
an element is accessed.

Get, put and remove operations take amortized constant time due to the
use of a hash map.
Precondition
pre debug : keys.length = values.length = nxtprv.length

Type Parameters

mutate effect to be used to create mutable variables
type of the keys to the values in the cache
type of values stored in the cache

Functions

 => 
String
[Redefinition of  Any.as_string]
get a string representation of this cache
showing key value pairs in order from most to least recently accessed

redefines:

the capacity of the cache,
i.e. the maximum number of elements it can hold at the same time
(R 
type
, F 
type
: Typed_Function R, f F)
 => 
R
[Inherited from  Any]
dynamic_apply -- apply `f.call` to `Any.this`'s dynamic type and value

This can be used to perform operation on values depending on their dynamic
type.

Here is an example that takes a `Sequence Any` that may contain boxed values
of types `i32` and `f64`. We can now write a feature `get_f64` that extracts
these values converted to `f64` and build a function `sum` that sums them up
as follows:


 => 
Type
[Inherited from  Any]
Get the dynamic type of this instance. For value instances `x`, this is
equal to `type_of x`, but for `x` with a `ref` type `x.dynamic_type` gives
the actual runtime type, while `type_of x` results in the static
compile-time type.

There is no dynamic type of a type instance since this would result in an
endless hierarchy of types. So for Type values, dynamic_type is redefined
to just return Type.type.
(key K)
 => 
option V
get value for given key
is this cache currently empty, i.e. not storing any elements?
 => 
String
[Inherited from  Any]
convenience prefix operator to create a string from a value.

This permits usage of `$` as a prefix operator in a similar way both
inside and outside of constant strings: $x and "$x" will produce the
same string.
(key K, value V)
 => 
unit
add or update value for given key
remove value for given key from the cache,
returns the value if the key existed
the number of elements currently in the cache

Type Features

 => 
String
[Inherited from  Type]
string representation of this type to be used for debugging.

result has the form "<name>", but this might change in the future

redefines:

 => 
Type
[Inherited from  Type]
There is no dynamic type of a type instance since this would result in an
endless hierarchy of types, so dynamic_type is redefined to just return
Type.type here.

Note: Typechecking is undecidable when 'type' is a type, Mark B. Reinhold, 1989
see: https://dspace.mit.edu/bitstream/handle/1721.1/149366/MIT-LCS-TR-458.pdf?sequence=6

redefines:

(T 
type
)
 => 
bool
[Inherited from  Type]
Is this type assignable to a type parameter with constraint `T`?

The result of this is a compile-time constant that can be used to specialize
code for a particular type.


it is most useful in conjunction with preconditions or `if` statements as in


or

 => 
String
[Inherited from  Type]
name of this type, including type parameters, e.g. 'option (list i32)'.
create an empty LRU cache with the given capacity
 => 
String
[Inherited from  Type]
convenience prefix operator to create a string from a value.

This permits usage of `$` as a prefix operator in a similar way both
inside and outside of constant strings: $x and "$x" will produce the
same string.

NYI: Redefinition allows the type feature to be distinguished from its normal counterpart, see #3913

redefines:

 => 
Type
[Inherited from  Any]
Get a type as a value.

This is a feature with the effect equivalent to Fuzion's `expr.type` call tail.
It is recommended to use `expr.type` and not `expr.type_value`.

`type_value` is here to show how this can be implemented and to illustrate the
difference to `dynamic_type`.
0.099dev (GIT hash 02118e9cbed77f3897084a4a507da3f11ac8881e)
last changed: 2026-09-02