检查是否为 null 并为其分配值的快捷方式？
Short cut for a check for null and assigning a value to it if it is?
有了新的 C# 8 功能，此代码结构现在有捷径：
if (App.selectedPhrases == null)
App.selectedPhrases = App.DB.GetSelectedPhrases();
App.selectedPhrases ??= App.DB.GetSelectedPhrases();
是的，叫做Null-coalescing assignment:
App.selectedPhrases ??= App.DB.GetSelectedPhrases();
C# 8.0 introduces the null-coalescing assignment operator ??=. You can use the ??= operator to assign the value of its right-hand operand to its left-hand operand only if the left-hand operand evaluates to null.
有了新的 C# 8 功能，此代码结构现在有捷径：
if (App.selectedPhrases == null)
App.selectedPhrases = App.DB.GetSelectedPhrases();
App.selectedPhrases ??= App.DB.GetSelectedPhrases();
是的，叫做Null-coalescing assignment:
App.selectedPhrases ??= App.DB.GetSelectedPhrases();
C# 8.0 introduces the null-coalescing assignment operator ??=. You can use the ??= operator to assign the value of its right-hand operand to its left-hand operand only if the left-hand operand evaluates to null.