这是在 golang 中铸造吗? [英] Is this casting in golang?

问题描述

paxPayment, ok = dataObject.(*entities.PassengerPayment)

括号是干什么用的?我不确定这个赋值操作发生了什么.

What are the brackets used for? I'm not sure what is going on in this assignment operation.

你需要更多细节来回答这个问题吗?

Do you need any more details to answer this question?

推荐答案

这是一个类型断言.类型断言可用于:

It's a Type assertion. A type assertion can be used to:

• 从 interface 类型的值中获取 concrete 类型的值
• 或获取与初始接口类型不同的值(具有不同 方法集，实际上不是原始方法的子集，因为可以简单地使用简单类型 转化).

• obtain a value of concrete type from a value of interface type
• or to obtain a value of a different interface type than the initial one (an interface with a different method set, practically not subset of the original one as that could simply be obtained using a simple type conversion).

引用规范:

对于接口类型的表达式x和类型T，主表达式

For an expression x of interface type and a type T, the primary expression

x.(T)

断言 x 不是 nil 并且 x 中存储的值是 T 类型.符号 x.(T) 被称为类型断言.

asserts that x is not nil and that the value stored in x is of type T. The notation x.(T) is called a type assertion.

更准确地说，如果 T 不是接口类型，x.(T) 断言 x 的动态类型是 与 T 类型相同.在这种情况下，T 必须实现<代码>x;否则类型断言无效，因为 x 不可能存储 T 类型的值.如果T是接口类型，x.(T)断言x的动态类型实现了接口T.

More precisely, if T is not an interface type, x.(T) asserts that the dynamic type of x is identical to the type T. In this case, T must implement the (interface) type of x; otherwise the type assertion is invalid since it is not possible for x to store a value of type T. If T is an interface type, x.(T) asserts that the dynamic type of x implements the interface T.

更具体地说，您的示例是它的一种特殊形式，它还报告类型断言是否成立.如果不是，ok 将是 false，如果断言成立，ok 将是 true.

More specifically your example is a special form of it which also reports whether the type assertion holds. If not, ok will be false, and if the assertion holds, ok will be true.

这种特殊的形式与以下形式不同:

This special form never panics unlike the form of:

paxPayment = dataObject.(*entities.PassengerPayment)

如果 dataObject 不持有 *entities.PassengerPayment 类型的值，将会发生恐慌.

Which if dataObject does not hold a value of type *entities.PassengerPayment will panic.

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