From 94d207f4b27ba45b8d33e7e73d0829074a02117d Mon Sep 17 00:00:00 2001 From: Guillaume Gomez Date: Thu, 19 Dec 2019 13:45:36 +0100 Subject: [PATCH] Clean up E0121 long explanation --- src/librustc_error_codes/error_codes/E0121.md | 24 +++++++++++++++---- 1 file changed, 19 insertions(+), 5 deletions(-) diff --git a/src/librustc_error_codes/error_codes/E0121.md b/src/librustc_error_codes/error_codes/E0121.md index 069d0fc48fb0..6c20b2803cbe 100644 --- a/src/librustc_error_codes/error_codes/E0121.md +++ b/src/librustc_error_codes/error_codes/E0121.md @@ -1,10 +1,24 @@ -In order to be consistent with Rust's lack of global type inference, -type and const placeholders are disallowed by design in item signatures. +The type placeholder `_` was used withing a type on an item's signature. -Examples of this error include: +Erroneous code example: ```compile_fail,E0121 -fn foo() -> _ { 5 } // error, explicitly write out the return type instead +fn foo() -> _ { 5 } // error -static BAR: _ = "test"; // error, explicitly write out the type instead +static BAR: _ = "test"; // error +``` + +In those cases, you need to provide the type explicitly: + +``` +fn foo() -> i32 { 5 } // ok! + +static BAR: &str = "test"; // ok! +``` + +The type placeholder `_` can be used outside item's signature as follows: + +``` +let x = "a4a".split('4') + .collect::>(); // No need to precise the Vec's generic type. ```