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stashValue -- stash values of functions in their arguments

Synopsis

Usage:

((stashValue KEY) f) x
Inputs:
- KEY
- f, a function
- x, a mutable hash table, an argument for f
Outputs:
- The value of f x is returned, but the value is saved in x#KEY and not recomputed later. However, if the value found in x#KEY is an a cache function, such as is returned by (stashValue KEY) f, then the value of x#KEY x is returned instead, after first removing x#KEY from x.

Description

i1 : x = new MutableHashTable from { val => 1000 }

o1 = MutableHashTable{...1...}

o1 : MutableHashTable

i2 : f = (t -> (print "hi there"; t.val^4))

o2 = f

o2 : FunctionClosure

i3 : h = (stashValue VALUE) f

o3 = -*a cache function*-

o3 : CacheFunction

i4 : h x
hi there

o4 = 1000000000000

i5 : h x

o5 = 1000000000000

i6 : peek x

o6 = MutableHashTable{val => 1000           }
                      VALUE => 1000000000000

Code

../../../../../Macaulay2/m2/methods.m2:674:17-682:25: --source code:
stashValue = key -> f -> new CacheFunction from (x -> (
          if x#?key then (
               val := x#key;
               if class val === CacheFunction then (
                    remove(x,key);
                    x#key = val x)
               else val
               )
          else x#key = f x))

See also

cacheValue -- cache values of functions in their arguments

For the programmer

The object stashValue is a function closure.