From c34ad2d537e41c9b31e240aa1e6fadd994115a16 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= Date: Thu, 15 Apr 2010 10:18:53 +0200 Subject: Silence warnings for expressions that are assigned to "_" There is currently no zero-cost way to silence the warning "the result of the expression is ignored", which is issued for code such as: list_to_integer(S), ok Such code can be useful for assertions or input validation. Teach the compiler to silence the warning for expressions that are explicitly assigned to to the "_" variable, such as: _ = list_to_integer(S), ok Implement it by having the v3_core pass annotate calls in Core Erlang like this: let <_> = ( call 'erlang':'list_to_integer'(S) -| ['result_not_wanted'] ) in 'ok' and modifiy sys_core_fold to suppress the warning for any call having the annotation. We deliberately do not make it possible to silence the warnings for expressions like: {build,an,unnecessary,term}, ok or is_list(L), ok because we don't know of any real-world scenarios in which that would be useful. --- lib/compiler/test/match_SUITE.erl | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) (limited to 'lib/compiler/test/match_SUITE.erl') diff --git a/lib/compiler/test/match_SUITE.erl b/lib/compiler/test/match_SUITE.erl index 20969c0b26..7d5669025c 100644 --- a/lib/compiler/test/match_SUITE.erl +++ b/lib/compiler/test/match_SUITE.erl @@ -21,14 +21,14 @@ -export([all/1, pmatch/1,mixed/1,aliases/1,match_in_call/1, untuplify/1,shortcut_boolean/1,letify_guard/1, - selectify/1]). + selectify/1,underscore/1]). -include("test_server.hrl"). all(suite) -> test_lib:recompile(?MODULE), [pmatch,mixed,aliases,match_in_call,untuplify,shortcut_boolean, - letify_guard,selectify]. + letify_guard,selectify,underscore]. pmatch(Config) when is_list(Config) -> ?line ok = doit(1), @@ -352,4 +352,16 @@ sel_same_value2(V) when V =:= 42; V =:= 43 -> sel_same_value2(_) -> error. +underscore(Config) when is_list(Config) -> + case Config of + [] -> + %% Assignment to _ at the end of a construct. + _ = length(Config); + [_|_] -> + %% Assignment to _ at the end of a construct. + _ = list_to_tuple(Config) + end, + _ = is_list(Config), + ok. + id(I) -> I. -- cgit v1.2.3