From 5d0874a8f9fd617308d9024783db1e4e24268184 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Micha=C5=82=20Muska=C5=82a?= Date: Fri, 27 Apr 2018 12:40:07 +0200 Subject: Introduce is_map_key/2 guard BIF This complements the `map_get/2` guard BIF introduced in #1784. Rationale. `map_get/2` allows accessing map fields in guards, but it might be problematic in more complex guard expressions, for example: foo(X) when map_get(a, X) =:= 1 or is_list(X) -> ... The `is_list/1` part of the guard could never succeed since the `map_get/2` guard would fail the whole guard expression. In this situation, this could be solved by using `;` instead of `or` to separate the guards, but it is not possible in every case. To solve this situation, this PR proposes a `is_map_key/2` guard that allows to check if a map has key inside a guard before trying to access that key. When combined with `is_map/1` this allows to construct a purely boolean guard expression testing a value of a key in a map. Implementation. Given the use case motivating the introduction of this function, the PR contains compiler optimisations that produce optimial code for the following guard expression: foo(X) when is_map(X) and is_map_key(a, X) and map_get(a, X) =:= 1 -> ok; foo(_) -> error. Given all three tests share the failure label, the `is_map_key/2` and `is_map/2` tests are optimised away. As with `map_get/2` the `is_map_key/2` BIF is allowed in match specs. --- lib/stdlib/src/erl_internal.erl | 2 ++ 1 file changed, 2 insertions(+) (limited to 'lib/stdlib/src/erl_internal.erl') diff --git a/lib/stdlib/src/erl_internal.erl b/lib/stdlib/src/erl_internal.erl index 6d3d5baa23..dd509191ef 100644 --- a/lib/stdlib/src/erl_internal.erl +++ b/lib/stdlib/src/erl_internal.erl @@ -109,6 +109,7 @@ new_type_test(is_function, 2) -> true; new_type_test(is_integer, 1) -> true; new_type_test(is_list, 1) -> true; new_type_test(is_map, 1) -> true; +new_type_test(is_map_key, 2) -> true; new_type_test(is_number, 1) -> true; new_type_test(is_pid, 1) -> true; new_type_test(is_port, 1) -> true; @@ -315,6 +316,7 @@ bif(is_function, 2) -> true; bif(is_integer, 1) -> true; bif(is_list, 1) -> true; bif(is_map, 1) -> true; +bif(is_map_key, 2) -> true; bif(is_number, 1) -> true; bif(is_pid, 1) -> true; bif(is_port, 1) -> true; -- cgit v1.2.3