problem with ruby19's Hash behavior

[Aaron]

see the following codes pls, I wonder if this's a intent or a bug. For me the first line sounds better having same result with the later line

[1].inject(Hash.new {[]}){ |result, i| result[:mem] << i; result } => {}
[1].inject(Hash.new {[]}){ |result, i| result[:mem] <<= i; result }

=> {:mem=>[1]}

P.S. coding with ruby 1.9.2p180 atm

 

[Roger Braun]

Hi Aaron

see the following codes pls, I wonder if this's a intent or a bug. For me=

the first line sounds better having same result with the later line

[1].inject(Hash.new {[]}){ |result, i| result[:mem] << i; =C2=A0 result=

}
=3D> {}

[1].inject(Hash.new {[]}){ |result, i| result[:mem] <<=3D i; result }

=3D> {:mem=3D>[1]}

It's the expected behaviour. See
http://ruby-doc.org/core/classes/Hash.html#M000718.

"If a block is specified, it will be called with the hash object and
the key, and should return the default value. It is the block=E2=80=98s
responsibility to store the value in the hash if required."

[1].inject(Hash.new {|h,k| h[k] =3D Array.new}){ |result, i|
result[:mem] << i; result }
=3D> {:mem=3D>[1]}

--=20
Roger Braun
rbraun.net | humoralpathologie.de

 

[Roy Zuo]

Hi,

I still cannot understand.

In the first example, result[:mem] should be [ ] before "result[:mem] << i" is
executed. Afterwards it should be [1], and the return value should be {:mem =>
[1]}.

In the second example, what does "<<=" stand for?

Roy

Hi Aaron

see the following codes pls, I wonder if this's a intent or a bug. For me the first line sounds better having same result with the later line

[1].inject(Hash.new {[]}){ |result, i| result[:mem] << i;   result } => {}
[1].inject(Hash.new {[]}){ |result, i| result[:mem] <<= i; result }

=> {:mem=>[1]}

It's the expected behaviour. See
http://ruby-doc.org/core/classes/Hash.html#M000718.

"If a block is specified, it will be called with the hash object and
the key, and should return the default value. It is the block‘s
responsibility to store the value in the hash if required."

[1].inject(Hash.new {|h,k| h[k] = Array.new}){ |result, i|
result[:mem] << i; result }
=> {:mem=>[1]}

--