Const-does>
¶A frequent use of create
...does>
is for transferring
some values from definition-time to run-time. Other ways of achieving
this are closures (see Closures), and with colon definitions
(see User-defined defining words with colon definitions), but
another way of achieving this is to use
Defines name and returns.
name execution: pushes w*uw r*ur, then performs the
code following the const-does>
.
A typical use of this word is:
: curry+ ( n1 "name" -- ) 1 0 CONST-DOES> ( n2 -- n1+n2 ) + ; 3 curry+ 3+
Here the 1 0
means that 1 cell and 0 floats are transferred from
definition to run-time.
The advantages of using const-does>
compared to
create}...@word{does>
are:
does>
, you have to introduce a @
that cannot
be optimized away automatically (because the system does not know
whether you allow to access the data with >body
...!
).
You can address this problem with set-optimizer
(see User-defined compile,
), but const-does>
avoids
it; however, the current implementation is still not particularly
efficient.
A Standard Forth implementation of const-does>
is available in
compat/const-does.fs.