Ruby 块和无括号的参数 [英] Ruby block and unparenthesized arguments

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

Braces have a high precedence; do has a low precedence

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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