New function has.cache

[dkesh]

This commit creates a new function has.cache( f, ... ) that returns TRUE or FALSE

I use memoisation extensively for network operations. It is sometimes useful to me to use a slow API if it has already been cached and a faster API if the slow API has not been cached. In this case, I want to test whether a function has been cached without actually running it.

[jimhester]

Thanks for the PR! I renamed this function has_cache() and modified the API, it now returns a modified memoized function that simply returns a boolean value if the arguments have a cached value. This simplified the implementation (which has become more complicated after merging #14) and gives you the same auto completion of arguments. So from your example you can now do the following.

mem_sum <- memoise(sum)
has_cache(mem_sum)(1, 2, 3) # FALSE
#> [1] FALSE
mem_sum(1, 2, 3)
#> [1] 6
has_cache(mem_sum)(1, 2, 3) # TRUE
#> [1] TRUE

[dkesh]

Thanks!