懒惰初始化可空成员(Lazy initialization of nullable member)

如果我们将成员变量定义为

private var foo: Foo? = null

当我们调用带有参数的方法（初始化Foo时需要）时，我们想要初始化它，有没有比这更好的方法呢？

fun generateFoo(bar: Bar): Foo { var localFoo = foo if (localFoo == null) { localFoo = Foo(bar) foo = localFoo } return localFoo }

我正在考虑避免所有变量赋值。

编辑：这里的版本略短，但仍不理想

fun generateFoo(bar: Bar): Foo { var localFoo = foo ?: Foo(bar) foo = localFoo return localFoo }

If we have a member variable defined as

private var foo: Foo? = null

and we want to initialize it when we call a method with an argument (which is needed to initialize Foo), is there a better way to do it than this?

fun generateFoo(bar: Bar): Foo { var localFoo = foo if (localFoo == null) { localFoo = Foo(bar) foo = localFoo } return localFoo }

I'm looking at avoiding all the variable assignments.

Edit: a slightly shorter version is here, but still not ideal

fun generateFoo(bar: Bar): Foo { var localFoo = foo ?: Foo(bar) foo = localFoo return localFoo }

最满意答案

这是安全的，除非你有多个线程命中你的类：

fun generateFoo(bar: Bar): Foo { if (foo == null) { foo = Foo(bar) } return foo!! }

但是如果你愿意，你可以做这样的事情 - 取决于你是否认为这比你已经拥有的更长版本更具可读性：

fun generateFoo(bar: Bar) = foo ?: Foo(bar).also { foo = it }

This is safe unless you have multiple threads hitting your class:

fun generateFoo(bar: Bar): Foo { if (foo == null) { foo = Foo(bar) } return foo!! }

But if you like, you can do things like this - up to you whether you think this is more readable than the longer version you already have:

fun generateFoo(bar: Bar) = foo ?: Foo(bar).also { foo = it }懒惰初始化可空成员(Lazy initialization of nullable member)

如果我们将成员变量定义为

private var foo: Foo? = null

当我们调用带有参数的方法（初始化Foo时需要）时，我们想要初始化它，有没有比这更好的方法呢？

fun generateFoo(bar: Bar): Foo { var localFoo = foo if (localFoo == null) { localFoo = Foo(bar) foo = localFoo } return localFoo }

我正在考虑避免所有变量赋值。

编辑：这里的版本略短，但仍不理想

fun generateFoo(bar: Bar): Foo { var localFoo = foo ?: Foo(bar) foo = localFoo return localFoo }

If we have a member variable defined as

private var foo: Foo? = null

and we want to initialize it when we call a method with an argument (which is needed to initialize Foo), is there a better way to do it than this?

fun generateFoo(bar: Bar): Foo { var localFoo = foo if (localFoo == null) { localFoo = Foo(bar) foo = localFoo } return localFoo }

I'm looking at avoiding all the variable assignments.

Edit: a slightly shorter version is here, but still not ideal

fun generateFoo(bar: Bar): Foo { var localFoo = foo ?: Foo(bar) foo = localFoo return localFoo }

最满意答案

这是安全的，除非你有多个线程命中你的类：

fun generateFoo(bar: Bar): Foo { if (foo == null) { foo = Foo(bar) } return foo!! }

但是如果你愿意，你可以做这样的事情 - 取决于你是否认为这比你已经拥有的更长版本更具可读性：

fun generateFoo(bar: Bar) = foo ?: Foo(bar).also { foo = it }

This is safe unless you have multiple threads hitting your class:

fun generateFoo(bar: Bar): Foo { if (foo == null) { foo = Foo(bar) } return foo!! }

But if you like, you can do things like this - up to you whether you think this is more readable than the longer version you already have:

fun generateFoo(bar: Bar) = foo ?: Foo(bar).also { foo = it }