Julia约定的可选参数 [英] Julia convention for optional arguments

问题描述

说我有一个功能，例如f(x,y)，但是y参数是可选的.将y设置为可选参数的首选方法是什么?一种对我有用的选项:

Say I have a function such as f(x,y) but the y parameter is optional. What is the preferred way to set y as an optional argument? One option that works for me:

function f(x, y=nothing)
    # do stuff 
    if y == nothing
        # do stuff
    else
        # do stuff
    end
    # do stuff
end

但这是首选方法吗?我不能将y设置为用于计算的单个默认值，因为在y为空时，有许多计算方式不同.我也可以只具有单独的功能f(x)和f(x,y)，但这似乎太多了代码重复.

But is this the preferred way? I can't set y to a single default value to use in calculation, as there are a number of calculations that are done differently when y is nothing. I could also just have separate functions f(x) and f(x,y) but that seems like too much code duplication.

推荐答案

这很好.请注意，可选参数会导致分派.这意味着if y == nothing(或等效的if typeof(y) <: Void)实际上将被编译掉.您将获得两个不同的函数，这取决于用户是否提供值.因此，最后，if语句编译掉了，并且这样做非常有效.

This is fine. Note that optional arguments cause dispatch. This means that the if y == nothing (or equivalently, if typeof(y) <: Void), will actually compile away. You'll get two different functions which depend on whether the user gives a value or not. So in the end, the if statement compiles away and it's perfectly efficient to do this.

我会注意到，关键字参数目前并非如此.

I will note that the same is not currently true for keyword arguments.

执行此操作的另一种方法是使用两种方法:

Another way to do this is to have two methods:

f(x)

和

f(x,y)

两种方法是否比使用if的1种方法更好?取决于问题.由于if将使用类型信息进行编译，因此这两种方法除了代码组织之外没有其他区别.

Whether two methods is nicer than 1 method with an if depends on the problem. Since the if will compile away using type information, there's no difference between these two approaches other than code organization.

这篇关于Julia约定的可选参数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！