通過值捕獲（或 const 引用捕獲）傳進 lambda，會默認復制成 const。

背景

匿名函數外部定義 QSet<QString> nameSet,需要傳入匿名函數使用修改

connect(dlg, ..., [nameSet](...) {nameSet.insert(name); // ? 這里其實是 const QSet<QString>
});

所以報錯:

XXX.cpp:604:33: No matching member function for call to 'insert'
qset.h:155:21: candidate function not viable: 'this' argument has type 'const QSet<QString>', but method is not marked const
qset.h:157:21: candidate function not viable: 'this' argument has type 'const QSet<QString>', but method is not marked const
qset.h:179:14: candidate function not viable: requires 2 arguments, but 1 was provided

解決：

使用引用&捕獲

connect(dlg, ..., [&nameSet](...) {});