Re: What does '||=' mean?

On Sat, Apr 21, 2012 at 8:22 PM, David Heitzman <[e-mail]> wro=
te:
> Oh wow, =A0a subtle distinction, but important. I did not know.
>
> if the left hand side is non-nil then no assignment happens at all.

More subtleties: if the left hand side is non falseish (i.e. not nil
and not false) the assignment will happen.

irb(main):008:0> h=3D{:x=3D>false,:y=3D>nil}
=3D> {:x=3D>false, :y=3D>nil}
irb(main):009:0> h[:x] ||=3D 1
=3D> 1
irb(main):010:0> h[:y] ||=3D 2
=3D> 2
irb(main):011:0> h[:z] ||=3D 3
=3D> 3
irb(main):012:0> h
=3D> {:x=3D>1, :y=3D>2, :z=3D>3}

Note also that in case of a Hash the default value influences the result:

irb(main):016:0> h=3D{:x=3D>false,:y=3D>nil}
=3D> {:x=3D>false, :y=3D>nil}
irb(main):017:0> h.default =3D 99
=3D> 99
irb(main):018:0> h[:x] ||=3D 1
=3D> 1
irb(main):019:0> h[:y] ||=3D 2
=3D> 2
irb(main):020:0> h[:z] ||=3D 3
=3D> 99
irb(main):021:0> h
=3D> {:x=3D>1, :y=3D>2}

And, to make things more complicated, there's also a default_proc:

irb(main):022:0> h =3D Hash.new {|ha,k| ha[k]=3D88}.merge(:x=3D>false,:y=3D=
>nil)
=3D> {:x=3D>false, :y=3D>nil}
irb(main):023:0> h[:x] ||=3D 1
=3D> 1
irb(main):024:0> h[:y] ||=3D 2
=3D> 2
irb(main):025:0> h[:z] ||=3D 3
=3D> 88
irb(main):026:0> h
=3D> {:x=3D>1, :y=3D>2, :z=3D>88}


Kind regards

robert

--=20
remember.guy do |as, often| as.you_can - without end
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