diff options
| author | Michał Muskała <[email protected]> | 2018-04-27 12:40:07 +0200 |
|---|---|---|
| committer | Michał Muskała <[email protected]> | 2018-04-29 17:03:43 +0200 |
| commit | 5d0874a8f9fd617308d9024783db1e4e24268184 (patch) | |
| tree | ac61f2f0f8d7f7483af9e17df44b49aeb049e695 /lib/compiler/test | |
| parent | d423a7af502227afcdcf7d2a1efecded85ea95fb (diff) | |
| download | otp-5d0874a8f9fd617308d9024783db1e4e24268184.tar.gz otp-5d0874a8f9fd617308d9024783db1e4e24268184.tar.bz2 otp-5d0874a8f9fd617308d9024783db1e4e24268184.zip | |
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.
Diffstat (limited to 'lib/compiler/test')
| -rw-r--r-- | lib/compiler/test/map_SUITE.erl | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/lib/compiler/test/map_SUITE.erl b/lib/compiler/test/map_SUITE.erl index e98c295da6..6badc7a8b8 100644 --- a/lib/compiler/test/map_SUITE.erl +++ b/lib/compiler/test/map_SUITE.erl @@ -1203,12 +1203,18 @@ t_guard_bifs(Config) when is_list(Config) -> true = map_guard_empty_2(), true = map_guard_head(#{a=>1}), false = map_guard_head([]), + true = map_get_head(#{a=>1}), + false = map_get_head([]), + true = map_is_key_head(#{a=>1}), + false = map_is_key_head(#{}), true = map_guard_body(#{a=>1}), false = map_guard_body({}), true = map_guard_pattern(#{a=>1, <<"hi">> => "hi" }), false = map_guard_pattern("list"), true = map_guard_tautology(), true = map_guard_ill_map_size(), + true = map_field_check_sequence(#{a=>1}), + false = map_field_check_sequence(#{}), ok. map_guard_empty() when is_map(#{}); false -> true. @@ -1218,6 +1224,12 @@ map_guard_empty_2() when true; #{} andalso false -> true. map_guard_head(M) when is_map(M) -> true; map_guard_head(_) -> false. +map_get_head(M) when map_get(a, M) =:= 1 -> true; +map_get_head(_) -> false. + +map_is_key_head(M) when is_map_key(a, M) -> true; +map_is_key_head(M) -> false. + map_guard_body(M) -> is_map(M). map_guard_pattern(#{}) -> true; @@ -1227,6 +1239,12 @@ map_guard_tautology() when #{} =:= #{}; true -> true. map_guard_ill_map_size() when true; map_size(0) -> true. +map_field_check_sequence(M) + when is_map(M) andalso is_map_key(a, M) andalso (map_get(a, M) == 1) -> + true; +map_field_check_sequence(_) -> + false. + t_guard_sequence(Config) when is_list(Config) -> {1, "a"} = map_guard_sequence_1(#{seq=>1,val=>id("a")}), {2, "b"} = map_guard_sequence_1(#{seq=>2,val=>id("b")}), |