CODEWITHSUNDEEP
rubystruct
user3162553
user3162553

Reputation: 2859

Initializing Ruby Structs with Keyword arguments

Ruby version: 2.3.1

It does not appear that Ruby Structs can be declared using keyword params. Is there a way to do this within Struct?

Example:

MyStruct = Struct.new(:fname, :lname)
=> MyStruct

my_struct = MyStruct.new(fname: 'first', lname: 'last')
=> <struct MyStruct fname={:fname=>"first", :lname=>"last"}, lname=nil>

my_struct.fname
=> {:fname=>"first", :lname=>"last"}

my_struct.lname
=> nil

Upvotes: 14

Views: 6219

Answers (2)

Martinos
Martinos

Reputation: 2226

With Ruby 2.5, you can set the keyword_init option to true.

MyStruct = Struct.new(:fname, :lname, keyword_init: true)
# => MyStruct(keyword_init: true)
irb(main):002:0> my_struct = MyStruct.new(fname: 'first', lname: 'last')
# => #<struct MyStruct fname="first", lname="last">

Upvotes: 23

Cary Swoveland
Cary Swoveland

Reputation: 110675

my_struct = MyStruct.new(fname: 'first', lname: 'last')

is the same as

my_struct = MyStruct.new({ fname: 'first', lname: 'last' })
  #=> #<struct MyStruct fname={:fname=>"first", :lname=>"last"}, lname=nil>

(one argument) so fname is set equal to the argument and lname is set to nil, in the same way that x, y = [2]; x #=> 2; y #=> nil.

This is because Ruby allows one to omit the braces when a hash is the argument of a method.

You may wish to search SO for related questions such as this one.

Upvotes: 2

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