Description Usage Arguments Value See Also Examples
A mapper is a collection of functions that define how a type
of foreign object is accessed. newMapper
creates a new
mapper object, assigns it a type, and places it in the global
Mapper database.
1 |
type |
Character vector length one describing the unique type of foreign objects available through the new mapper. |
init |
A function whose signature is |
get |
A function whose signature is |
assign |
A function whose signature is |
finalize |
A function whose signature is |
... |
Additional objects that are also added to the mapper environment. They MUST be named arguments, i.e. name=val. |
Invisibly returns the new mapper, an object of class
'dataMapper'. newMapper
is called for its side effect of
adding the new mapper to the global Mapper database.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 | # Complete example mapper
newMapper(
type="EXAMPLE",
init=function(map,symbols=c('foo','bar','baz'),len=3){
# Install symbols that the users passes in from newMap().
lapply(symbols,install,map)
# Now let's add some state to the internal portion of our map.
map$len <- len
# Returning FALSE means failure
return(TRUE)
},
get = function(x) {
cat("I'll just get",x,"for you.\n")
# len is pulled from the internal portion of the map
# by lexical scoping rules. Anything can be returned here, but we
# default to a numeric value
rnorm(len)
},
assign = function(x,val){
cat("Calling assign",val,"to",x,".\n")
},
finalize = function(map){
cat("Finalization can clear any state, like shutting down database\n")
cat("connections, socket connections, etc.\n")
},
# The rest of the arguments are copied to the internal portion of the map.
foo = 'bar'
)
|
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