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/warnings_SUITE.erl | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'lib/compiler/test/warnings_SUITE.erl') diff --git a/lib/compiler/test/warnings_SUITE.erl b/lib/compiler/test/warnings_SUITE.erl index 6e60ab88cb..8b98db54f2 100644 --- a/lib/compiler/test/warnings_SUITE.erl +++ b/lib/compiler/test/warnings_SUITE.erl @@ -375,7 +375,12 @@ effect(Config) when is_list(Config) -> comp_op -> X =:= 2; cookie -> - erlang:get_cookie() + erlang:get_cookie(); + result_ignore -> + _ = list_to_integer(X); + warn_lc_4 -> + %% No warning because of assignment to _. + [_ = abs(Z) || Z <- [1,2,3]] end, ok. -- cgit v1.2.3