Ruby 块和无括号的参数

问题描述

我提取了一个简单的例子:

I extracted simple example:

require 'pp'
x = 1..3
pp x.map do |i| {:value => i, :double => (i*2)} end
pp x.map { |i| {:value => i, :double => (i*2)} }

pp(x.map do |i| {:value => i, :double => (i*2)} end)
pp(x.map { |i| {:value => i, :double => (i*2)} })

我想知道为什么第一个 pp 会产生:

I am wondering why first pp produces:

[1, 2, 3]

虽然所有的订单都在给:

While all the oders are giving:

[{:value=>1, :double=>2}, {:value=>2, :double=>4}, {:value=>3, :double=>6}]

我认为它与运算符优先级有关.我在哪里可以找到好的解释?

I assume it has something to do with operator precedence. Where can I find good explanation?

推荐答案

因为你在打电话

pp x.map

并将块传递给 pp(忽略它)

and passing a block to pp (which ignores it)

如编程 Ruby 一书中所述

大括号具有高优先级；do 的优先级较低

因此，有效地，大括号绑定到离它们最近的函数调用(x.map)，而 do 绑定到最远的函数调用(pp).这有点简单，但它应该可以解释这种情况

So, effectively, braces tie to the function call closest to them (x.map) whereas do binds to the furthest away (pp). That's a bit simplistic but it should explain this situation

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