ES.6: Declare names in for-statement initializers and conditions to limit scope
ES.6:將循環變量和條件變量定義在限定範圍內
Reason(原因)
Readability. Minimize resource retention.
可讀性。最小化資源佔用。
Example(示例)
<code>void use()
{
for (string s; cin >> s;)
v.push_back(s);
for (int i = 0; i < 20; ++i) { // good: i is local to for-loop
// ...
}
if (auto pc = dynamic_cast<circle>(ps)) { // good: pc is local to if-statement
// ... deal with Circle ...
}
else {
// ... handle error ...
}
}/<circle>/<code>
Enforcement(實施建議)
- Flag loop variables declared before the loop and not used after the loop
- 標記在循環之前定義循環變量而在循環之後沒有使用的情況。
- (hard) Flag loop variables declared before the loop and used after the loop for an unrelated purpose.
- (困難)標記在循環之前定義循環變量,然後在循環之後用於無關目的的情況。
C++17 and C++20 example(C++17和C++20示例)
Note: C++17 and C++20 also add if, switch, and range-for initializer statements. These require C++17 and C++20 support.
注意:C++17和C++20也增加了if,switch,和範圍for初始化語句。下面的代碼需要C++17和C++20支持。
<code>mapmymap; /<code>
if (auto result = mymap.insert(value); result.second) {
// insert succeeded, and result is valid for this block
use(result.first); // ok
// ...
} // result is destroyed here
C++17 and C++20 enforcement (if using a C++17 or C++20 compiler)
C++17和C++20實施建議(如果使用C++17或者C++20編譯器)
- Flag selection/loop variables declared before the body and not used after the body
- 標記在選擇/循環體之前定義選擇/循環變量而在選擇/循環體之後沒有使用的情況。
- (hard) Flag selection/loop variables declared before the body and used after the body for an unrelated purpose.
- (困難)標記在選擇/循環體之前定義選擇/循環變量,然後在選擇/循環體之後用於無關目的的情況。
原文鏈接
https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#es6-declare-names-in-for-statement-initializers-and-conditions-to-limit-scope
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