Updated 2015-01-31 04:09:21 by aspect

One caching strategy is to retain the X most-recently-referenced items and discard any additional items.

The examples on this page show a way of implementing with a simple proc: a TclOO solution would encapsulate the MRU operation a little more tidily. Another approach might use a write trace to limit the MRU's size. These alternatives are left as an exercise for the interested reader (.. who might want to add them to this page!)

MRU List  edit

An MRU list is straightforward .. the only decision is whether you want items stored in chronological or reverse-chronological order.
# most-recent-first
proc mrulist {listName limit args} {
    upvar 1 $listName list
    incr limit -1   ;# because list indexing counts from 0
    set list [lrange [linsert $list 0 {*}$args] 0 $limit]
}

# most-recent-last
proc mrulist {listName limit args} {
    upvar 1 $listName list
    incr limit -1   ;# because list indexing counts from 0
    lappend list {*}$args
    set list [lrange $list end-$limit end]
}

# Example:
while {[gets $chan line] > 0} {
    mrulist history 10 $line
}
puts "Last 10 entries:"
puts [join $history \n]

MRU Dict  edit

In "high performance" MRU-list ..., comp.lang.tcl, 2015-01-21, [Christian Gollwitzer] suggests an implementation of most-recently used that takes advantage of the order-preserving operation of dicts. Here is the suggestion, slightly modified to be more general:
proc pushmru {name limit args} {
    upvar $name dict
    foreach key $args {
        dict unset dict $key 
        dict set dict $key {}
        while {[dict size $dict] > $limit} {
            dict unset dict [lindex [dict keys $dict] 0]
        }
    }
    return $dict
}

Example
set i 0
while {[incr i] < 20} {
    pushmru cache 4 key$i
}