From 0b58d04fdedf09d4642a37631c972432ab5bced7 Mon Sep 17 00:00:00 2001 From: Bjarne Stroustrup Date: Mon, 10 Apr 2017 15:57:38 -0400 Subject: [PATCH] ES.84 --- CppCoreGuidelines.md | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) diff --git a/CppCoreGuidelines.md b/CppCoreGuidelines.md index 68bba56..9c1a047 100644 --- a/CppCoreGuidelines.md +++ b/CppCoreGuidelines.md @@ -8967,6 +8967,7 @@ Statement rules: * [ES.77: Minimize the use of 'break' and `continue` in loops](#Res-continue) * [ES.78: Always end a non-empty `case` with a `break`](#Res-break) * [ES.79: Use `default` to handle common cases (only)](#Res-default) +* [ES.84: Don't (try to) declare a local variable with no name](#Res-noname) * [ES.85: Make empty statements visible](#Res-empty) * [ES.86: Avoid modifying loop control variables inside the body of raw for-loops](#Res-loop-counter) @@ -10541,6 +10542,35 @@ Flag `switch`-statements over an enumeration that don't handle all enumerators a This may yield too many false positives in some code bases; if so, flag only `switch`es that handle most but not all cases (that was the strategy of the very first C++ compiler). +### ES.84: Don't (try to) declare a local variable with no name + +##### Reason + +There is no such thing. +What looks to a human like a variable without a name is to the compiler a statement consisting of a temporary that immediately goes out of scope. +To avoid unpleasent surprises. + +###### Example, bad + + void f() + { + lock{mx}; // Bad + // ... + } + +This declares an unnamed `lock` object that immediately goes out of scope at the point of the semicolon. +This is not an uncommon mistake. +In particular, this particular example can lead to hard-to find race conditions. +There are exceedingly clever used of this "idiom", but they are far rarer than the mistakes. + +##### Note + + Unnamed function arguments are fine. + +##### Enforcement + + Flag statements that are just a temporary + ### ES.85: Make empty statements visible ##### Reason