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| 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 /erts/doc/src/match_spec.xml | |
| 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 'erts/doc/src/match_spec.xml')
| -rw-r--r-- | erts/doc/src/match_spec.xml | 23 |
1 files changed, 12 insertions, 11 deletions
diff --git a/erts/doc/src/match_spec.xml b/erts/doc/src/match_spec.xml index 888366b239..46a3daebe8 100644 --- a/erts/doc/src/match_spec.xml +++ b/erts/doc/src/match_spec.xml @@ -86,12 +86,12 @@ <c><![CDATA[is_list]]></c> | <c><![CDATA[is_number]]></c> | <c><![CDATA[is_pid]]></c> | <c><![CDATA[is_port]]></c> | <c><![CDATA[is_reference]]></c> | <c><![CDATA[is_tuple]]></c> | - <c><![CDATA[is_map]]></c> | <c><![CDATA[is_binary]]></c> | - <c><![CDATA[is_function]]></c> | <c><![CDATA[is_record]]></c> | - <c><![CDATA[is_seq_trace]]></c> | <c><![CDATA['and']]></c> | - <c><![CDATA['or']]></c> | <c><![CDATA['not']]></c> | - <c><![CDATA['xor']]></c> | <c><![CDATA['andalso']]></c> | - <c><![CDATA['orelse']]></c> + <c><![CDATA[is_map]]></c> | <c><![CDATA[is_map_key]]></c> | + <c><![CDATA[is_binary]]></c> | <c><![CDATA[is_function]]></c> | + <c><![CDATA[is_record]]></c> | <c><![CDATA[is_seq_trace]]></c> | + <c><![CDATA['and']]></c> | <c><![CDATA['or']]></c> | + <c><![CDATA['not']]></c> | <c><![CDATA['xor']]></c> | + <c><![CDATA['andalso']]></c> | <c><![CDATA['orelse']]></c> </item> <item>ConditionExpression ::= ExprMatchVariable | { GuardFunction } | { GuardFunction, ConditionExpression, ... } | TermConstruct @@ -168,11 +168,12 @@ <c><![CDATA[is_list]]></c> | <c><![CDATA[is_number]]></c> | <c><![CDATA[is_pid]]></c> | <c><![CDATA[is_port]]></c> | <c><![CDATA[is_reference]]></c> | <c><![CDATA[is_tuple]]></c> | - <c><![CDATA[is_map]]></c> | <c><![CDATA[is_binary]]></c> | - <c><![CDATA[is_function]]></c> | <c><![CDATA[is_record]]></c> | - <c><![CDATA['and']]></c> | <c><![CDATA['or']]></c> | - <c><![CDATA['not']]></c> | <c><![CDATA['xor']]></c> | - <c><![CDATA['andalso']]></c> | <c><![CDATA['orelse']]></c> + <c><![CDATA[is_map]]></c> | <c><![CDATA[map_is_key]]></c> | + <c><![CDATA[is_binary]]></c> | <c><![CDATA[is_function]]></c> | + <c><![CDATA[is_record]]></c> | <c><![CDATA['and']]></c> | + <c><![CDATA['or']]></c> | <c><![CDATA['not']]></c> | + <c><![CDATA['xor']]></c> | <c><![CDATA['andalso']]></c> | + <c><![CDATA['orelse']]></c> </item> <item>ConditionExpression ::= ExprMatchVariable | { GuardFunction } | { GuardFunction, ConditionExpression, ... } | TermConstruct |