main-apidocs-erlang-estdlib-erts-underscore-internal.md
An implementation of a subset of the Erlang/OTP erts_internal interface.
These functions are not meant to be called directly. They are helpers, called from code generated by the compiler. In particular mc_iterator/1 and mc_refill/1 implement map comprehensions (#{K => V || K := V <- M}), introduced in OTP 26. The generated bytecode is identical from OTP 26 to at least OTP 29.
| mc_iterator/1 | Start iterating over a map comprehension generator. | | mc_refill/1 | Advance a map comprehension iterator. |
mc_iterator(MapOrIter) -> Iter
MapOrIter = map() | maps:iterator()Iter = {term(), term(), maps:iterator()} | none | []MapOrIter: a map or a map iterator to iterate over
returns: the first association as {Key, Value, NextIterator}, none if the map or iterator is empty, or [] if the argument is not a valid generator
Start iterating over a map comprehension generator.
This function is a helper called from compiler generated code for map comprehensions. It must be kept compatible as long as code calling this helper can still be loaded.
mc_refill(IterMap) -> Iter
IterMap = nonempty_improper_list(non_neg_integer() | list(), map())Iter = {term(), term(), maps:iterator()} | noneIterMap: a map iterator to refill
returns: the next association as {Key, Value, NextIterator} or none
Advance a map comprehension iterator.
This function is a helper called from compiler generated code for map comprehensions. It must be kept compatible as long as code calling this helper can still be loaded.