`each_with_object` 块内的 `+=` 和 `<<` 之间的区别
Difference between `+=` and `<<` inside a block for `each_with_object`
我不得不更新一个数组，我在传递给 Array#each_with_object:
的块内的不同代码运行中使用了 += 和 <<
代码 1
(1..5).each_with_object([]) do |i, a|
puts a.inspect
a += [i]
end
输出：
[]
[]
[]
[]
[]
代码 2
(1..5).each_with_object([]) do |i, a|
puts a.inspect
a << [i]
end
输出：
[]
[1]
[1,2]
[1,2,3]
[1,2,3,4]
+= 运算符不会更新原始数组。为什么？我在这里错过了什么？
在each_with_object中，所谓的备忘录对象在迭代中很常见。您需要修改该对象才能做一些有意义的事情。 += 运算符是 + 和赋值的语法糖，它不会修改接收者，因此迭代没有效果。如果你使用像<<或push这样的方法，那么它就会生效。
另一方面，在inject中，所谓的memo对象就是block的return值，不需要修改对象，但是需要return 下一次迭代所需的值。
It is clear to me that += operator is not updating the original array. Why?
因为 the documentation 这么说（强调我的）：
ary + other_ary → new_ary
Concatenation — Returns a new array built by concatenating the two arrays together to produce a third array.
[ 1, 2, 3 ] + [ 4, 5 ] #=> [ 1, 2, 3, 4, 5 ]
a = [ "a", "b", "c" ]
c = a + [ "d", "e", "f" ]
c #=> [ "a", "b", "c", "d", "e", "f" ]
a #=> [ "a", "b", "c" ]
Note that
x += y
is the same as
x = x + y
This means that it produces a new array. As a consequence, repeated use of += on arrays can be quite inefficient.
See also #concat.
比较 <<
ary << obj → ary
Append—Pushes the given object on to the end of this array. This expression returns the array itself, so several appends may be chained together.
[ 1, 2 ] << "c" << "d" << [ 3, 4 ]
#=> [ 1, 2, "c", "d", [ 3, 4 ] ]
Array#+的文档明确说返回了一个new数组（实际上不少于四次）。这与 Ruby 中 + 方法的其他用法一致，例如Bignum#+, Fixnum#+, Complex#+, Rational#+, Float#+, Time#+, String#+, BigDecimal#+, Date#+, Matrix#+, Vector#+, Pathname#+, Set#+, and URI::Generic#+.
我不得不更新一个数组，我在传递给 Array#each_with_object:
+= 和 <<
代码 1
(1..5).each_with_object([]) do |i, a|
puts a.inspect
a += [i]
end
输出：
[]
[]
[]
[]
[]
代码 2
(1..5).each_with_object([]) do |i, a|
puts a.inspect
a << [i]
end
输出：
[]
[1]
[1,2]
[1,2,3]
[1,2,3,4]
+= 运算符不会更新原始数组。为什么？我在这里错过了什么？
在each_with_object中，所谓的备忘录对象在迭代中很常见。您需要修改该对象才能做一些有意义的事情。 += 运算符是 + 和赋值的语法糖，它不会修改接收者，因此迭代没有效果。如果你使用像<<或push这样的方法，那么它就会生效。
另一方面，在inject中，所谓的memo对象就是block的return值，不需要修改对象，但是需要return 下一次迭代所需的值。
It is clear to me that += operator is not updating the original array. Why?
因为 the documentation 这么说（强调我的）：
ary + other_ary→new_aryConcatenation — Returns a new array built by concatenating the two arrays together to produce a third array.
[ 1, 2, 3 ] + [ 4, 5 ] #=> [ 1, 2, 3, 4, 5 ] a = [ "a", "b", "c" ] c = a + [ "d", "e", "f" ] c #=> [ "a", "b", "c", "d", "e", "f" ] a #=> [ "a", "b", "c" ]Note that
x += yis the same as
x = x + yThis means that it produces a new array. As a consequence, repeated use of
+=on arrays can be quite inefficient.See also
#concat.
比较 <<
ary << obj→aryAppend—Pushes the given object on to the end of this array. This expression returns the array itself, so several appends may be chained together.
[ 1, 2 ] << "c" << "d" << [ 3, 4 ] #=> [ 1, 2, "c", "d", [ 3, 4 ] ]
Array#+的文档明确说返回了一个new数组（实际上不少于四次）。这与 Ruby 中 + 方法的其他用法一致，例如Bignum#+, Fixnum#+, Complex#+, Rational#+, Float#+, Time#+, String#+, BigDecimal#+, Date#+, Matrix#+, Vector#+, Pathname#+, Set#+, and URI::Generic#+.